From 717978388e013e451625e9c518b48e9aca92eb49 Mon Sep 17 00:00:00 2001
From: Noel De Martin <noel@moodle.com>
Date: Tue, 1 Mar 2022 11:47:57 +0100
Subject: [PATCH 1/2] MOBILE-3982 core: Extract CoreComponentsRegistry

---
 .../components/context-menu/context-menu.ts     |  3 ++-
 .../components/navbar-buttons/navbar-buttons.ts |  9 +++++----
 src/core/components/tabs-outlet/tabs-outlet.ts  |  3 +--
 src/core/components/tabs/tab.ts                 |  4 ++--
 src/core/core.module.ts                         |  2 ++
 src/core/services/utils/dom.ts                  | 17 +++++++++++------
 6 files changed, 23 insertions(+), 15 deletions(-)

diff --git a/src/core/components/context-menu/context-menu.ts b/src/core/components/context-menu/context-menu.ts
index e981e7500..157407562 100644
--- a/src/core/components/context-menu/context-menu.ts
+++ b/src/core/components/context-menu/context-menu.ts
@@ -20,6 +20,7 @@ import { CoreUtils } from '@services/utils/utils';
 import { Translate } from '@singletons';
 import { CoreContextMenuItemComponent } from './context-menu-item';
 import { CoreContextMenuPopoverComponent } from './context-menu-popover';
+import { CoreComponentsRegistry } from '@singletons/components-registry';
 
 /**
  * This component adds a button (usually in the navigation bar) that displays a context menu popover.
@@ -60,7 +61,7 @@ export class CoreContextMenuComponent implements OnInit, OnDestroy {
         // Calculate the unique ID.
         this.uniqueId = 'core-context-menu-' + CoreUtils.getUniqueId('CoreContextMenuComponent');
 
-        CoreDomUtils.storeInstanceByElement(elementRef.nativeElement, this);
+        CoreComponentsRegistry.register(elementRef.nativeElement, this);
     }
 
     /**
diff --git a/src/core/components/navbar-buttons/navbar-buttons.ts b/src/core/components/navbar-buttons/navbar-buttons.ts
index 48439908e..205ec43db 100644
--- a/src/core/components/navbar-buttons/navbar-buttons.ts
+++ b/src/core/components/navbar-buttons/navbar-buttons.ts
@@ -25,6 +25,7 @@ import {
 import { CoreLogger } from '@singletons/logger';
 import { CoreDomUtils } from '@services/utils/dom';
 import { CoreContextMenuComponent } from '../context-menu/context-menu';
+import { CoreComponentsRegistry } from '@singletons/components-registry';
 
 const BUTTON_HIDDEN_CLASS = 'core-navbar-button-hidden';
 
@@ -80,7 +81,7 @@ export class CoreNavBarButtonsComponent implements OnInit, OnDestroy {
         this.element = element.nativeElement;
         this.logger = CoreLogger.getInstance('CoreNavBarButtonsComponent');
 
-        CoreDomUtils.storeInstanceByElement(this.element, this);
+        CoreComponentsRegistry.register(this.element, this);
     }
 
     /**
@@ -154,11 +155,11 @@ export class CoreNavBarButtonsComponent implements OnInit, OnDestroy {
         }
 
         const mainContextMenu = buttonsContainer.querySelector('core-context-menu');
-        const secondaryContextMenuInstance = CoreDomUtils.getInstanceByElement<CoreContextMenuComponent>(secondaryContextMenu);
-        let mainContextMenuInstance: CoreContextMenuComponent | undefined;
+        const secondaryContextMenuInstance = CoreComponentsRegistry.resolve(secondaryContextMenu, CoreContextMenuComponent);
+        let mainContextMenuInstance: CoreContextMenuComponent | null;
         if (mainContextMenu) {
             // Both containers have a context menu. Merge them to prevent having 2 menus at the same time.
-            mainContextMenuInstance = CoreDomUtils.getInstanceByElement<CoreContextMenuComponent>(mainContextMenu);
+            mainContextMenuInstance = CoreComponentsRegistry.resolve(mainContextMenu, CoreContextMenuComponent);
         } else {
             // There is a context-menu in these buttons, but there is no main context menu in the header.
             // Create one main context menu dynamically.
diff --git a/src/core/components/tabs-outlet/tabs-outlet.ts b/src/core/components/tabs-outlet/tabs-outlet.ts
index d7575f2fe..32f0f7872 100644
--- a/src/core/components/tabs-outlet/tabs-outlet.ts
+++ b/src/core/components/tabs-outlet/tabs-outlet.ts
@@ -29,7 +29,6 @@ import { Subscription } from 'rxjs';
 import { CoreUtils } from '@services/utils/utils';
 import { Params } from '@angular/router';
 import { CoreNavBarButtonsComponent } from '../navbar-buttons/navbar-buttons';
-import { CoreDomUtils } from '@services/utils/dom';
 import { StackEvent } from '@ionic/angular/directives/navigation/stack-utils';
 import { CoreNavigator } from '@services/navigator';
 import { CoreTabBase, CoreTabsBaseComponent } from '@classes/tabs';
@@ -188,7 +187,7 @@ export class CoreTabsOutletComponent extends CoreTabsBaseComponent<CoreTabsOutle
     protected showHideNavBarButtons(activatedPageName: string): void {
         const elements = this.ionTabs.outlet.nativeEl.querySelectorAll('core-navbar-buttons');
         elements.forEach((element) => {
-            const instance = CoreDomUtils.getInstanceByElement<CoreNavBarButtonsComponent>(element);
+            const instance = CoreComponentsRegistry.resolve(element, CoreNavBarButtonsComponent);
 
             if (instance) {
                 const pagetagName = element.closest('.ion-page')?.tagName;
diff --git a/src/core/components/tabs/tab.ts b/src/core/components/tabs/tab.ts
index 0fb0865fb..2d3166fd5 100644
--- a/src/core/components/tabs/tab.ts
+++ b/src/core/components/tabs/tab.ts
@@ -15,8 +15,8 @@
 import { Component, Input, Output, OnInit, OnDestroy, ElementRef, EventEmitter, ContentChild, TemplateRef } from '@angular/core';
 import { CoreTabBase } from '@classes/tabs';
 
-import { CoreDomUtils } from '@services/utils/dom';
 import { CoreUtils } from '@services/utils/utils';
+import { CoreComponentsRegistry } from '@singletons/components-registry';
 import { CoreNavBarButtonsComponent } from '../navbar-buttons/navbar-buttons';
 import { CoreTabsComponent } from './tabs';
 
@@ -144,7 +144,7 @@ export class CoreTabComponent implements OnInit, OnDestroy, CoreTabBase {
     protected showHideNavBarButtons(show: boolean): void {
         const elements = this.element.querySelectorAll('core-navbar-buttons');
         elements.forEach((element) => {
-            const instance = CoreDomUtils.getInstanceByElement<CoreNavBarButtonsComponent>(element);
+            const instance = CoreComponentsRegistry.resolve(element, CoreNavBarButtonsComponent);
 
             if (instance) {
                 instance.forceHide(!show);
diff --git a/src/core/core.module.ts b/src/core/core.module.ts
index d5c75b618..aa68a6e2a 100644
--- a/src/core/core.module.ts
+++ b/src/core/core.module.ts
@@ -51,9 +51,11 @@ import { CoreUpdateManagerProvider } from '@services/update-manager';
 import { CoreUrlUtilsProvider } from '@services/utils/url';
 import { CoreUtilsProvider } from '@services/utils/utils';
 import { CoreWSProvider } from '@services/ws';
+import { CoreComponentsRegistry } from '@singletons/components-registry';
 
 export const CORE_SERVICES: Type<unknown>[] = [
     CoreAppProvider,
+    CoreComponentsRegistry,
     CoreConfigProvider,
     CoreCronDelegateService,
     CoreCustomURLSchemesProvider,
diff --git a/src/core/services/utils/dom.ts b/src/core/services/utils/dom.ts
index 47c013e9c..a84b182df 100644
--- a/src/core/services/utils/dom.ts
+++ b/src/core/services/utils/dom.ts
@@ -52,6 +52,7 @@ import { CoreSites } from '@services/sites';
 import { NavigationStart } from '@angular/router';
 import { filter } from 'rxjs/operators';
 import { Subscription } from 'rxjs';
+import { CoreComponentsRegistry } from '@singletons/components-registry';
 
 /*
  * "Utils" service with helper functions for UI, DOM elements and HTML code.
@@ -68,7 +69,6 @@ export class CoreDomUtilsProvider {
     protected template: HTMLTemplateElement = document.createElement('template'); // A template element to convert HTML to element.
 
     protected matchesFunctionName?: string; // Name of the "matches" function to use when simulating a closest call.
-    protected instances: WeakMap<Element, unknown> = new WeakMap(); // Store component/directive instances indexed by element.
     protected debugDisplay = false; // Whether to display debug messages. Store it in a variable to make it synchronous.
     protected displayedAlerts: Record<string, HTMLIonAlertElement> = {}; // To prevent duplicated alerts.
     protected displayedModals: Record<string, HTMLIonModalElement> = {}; // To prevent duplicated modals.
@@ -671,9 +671,10 @@ export class CoreDomUtilsProvider {
      *
      * @param element The root element of the component/directive.
      * @return The instance, undefined if not found.
+     * @deprecated since 4.0.0. Use CoreComponentsRegistry instead.
      */
     getInstanceByElement<T = unknown>(element: Element): T | undefined {
-        return this.instances.get(element) as T;
+        return CoreComponentsRegistry.resolve<T>(element) ?? undefined;
     }
 
     /**
@@ -892,19 +893,22 @@ export class CoreDomUtilsProvider {
      * Remove a component/directive instance using the DOM Element.
      *
      * @param element The root element of the component/directive.
+     * @deprecated since 4.0.0. It's no longer necessary to remove instances.
      */
+    // eslint-disable-next-line @typescript-eslint/no-unused-vars
     removeInstanceByElement(element: Element): void {
-        const id = element.getAttribute(this.INSTANCE_ID_ATTR_NAME);
-        id && delete this.instances[id];
+        //
     }
 
     /**
      * Remove a component/directive instance using the ID.
      *
      * @param id The ID to remove.
+     * @deprecated since 4.0.0. It's no longer necessary to remove instances.
      */
+    // eslint-disable-next-line @typescript-eslint/no-unused-vars
     removeInstanceById(id: string): void {
-        delete this.instances[id];
+        //
     }
 
     /**
@@ -1664,9 +1668,10 @@ export class CoreDomUtilsProvider {
      *
      * @param element The root element of the component/directive.
      * @param instance The instance to store.
+     * @deprecated since 4.0.0. Use CoreComponentsRegistry instead.
      */
     storeInstanceByElement(element: Element, instance: unknown): void {
-        this.instances.set(element, instance);
+        CoreComponentsRegistry.register(element, instance);
     }
 
     /**

From 6b5d1db43c8b1eb2241fcb9a5bfe3b36ec8fbaa7 Mon Sep 17 00:00:00 2001
From: Noel De Martin <noel@moodle.com>
Date: Thu, 24 Feb 2022 17:23:22 +0100
Subject: [PATCH 2/2] MOBILE-3982 core: Refactor collapsible-header

---
 src/addons/calendar/pages/event/event.html    |   3 +-
 .../components/tabs-outlet/tabs-outlet.ts     |  14 +-
 src/core/directives/collapsible-header.ts     | 603 +++++++++---------
 src/core/directives/format-text.ts            |  19 +
 .../module-info/core-course-module-info.html  |   2 +-
 .../module-summary/module-summary.scss        |   2 +-
 .../components/single-activity.scss           |   2 +-
 .../features/course/pages/index/index.html    |   4 +-
 src/core/features/course/pages/index/index.ts |   4 +-
 src/core/singletons/components-registry.ts    |  53 ++
 src/theme/components/collapsible-header.scss  |  86 +++
 src/theme/globals.mixins.scss                 |  17 +-
 src/theme/theme.base.scss                     |  82 ---
 src/theme/theme.scss                          |   1 +
 14 files changed, 489 insertions(+), 403 deletions(-)
 create mode 100644 src/core/singletons/components-registry.ts
 create mode 100644 src/theme/components/collapsible-header.scss

diff --git a/src/addons/calendar/pages/event/event.html b/src/addons/calendar/pages/event/event.html
index ae1306688..39364fbc8 100644
--- a/src/addons/calendar/pages/event/event.html
+++ b/src/addons/calendar/pages/event/event.html
@@ -40,8 +40,7 @@
         </ion-card>
 
         <ion-list *ngIf="event">
-            <ion-item class="collapsible-title ion-text-wrap addon-calendar-event"
-                [ngClass]="['addon-calendar-eventtype-'+event.eventtype]">
+            <ion-item class="ion-text-wrap addon-calendar-event" collapsible [ngClass]="['addon-calendar-eventtype-'+event.eventtype]">
                 <core-mod-icon *ngIf="event.moduleIcon" [modicon]="event.moduleIcon" [showAlt]="false" [modname]="event.modulename"
                     [componentId]="event.instance" slot="start"></core-mod-icon>
                 <ion-icon *ngIf=" event.eventIcon && !event.moduleIcon" [name]="event.eventIcon" aria-hidden="true" slot="start">
diff --git a/src/core/components/tabs-outlet/tabs-outlet.ts b/src/core/components/tabs-outlet/tabs-outlet.ts
index 32f0f7872..e2ffef98f 100644
--- a/src/core/components/tabs-outlet/tabs-outlet.ts
+++ b/src/core/components/tabs-outlet/tabs-outlet.ts
@@ -23,7 +23,7 @@ import {
     ElementRef,
     SimpleChange,
 } from '@angular/core';
-import { IonTabs, ViewDidEnter, ViewDidLeave } from '@ionic/angular';
+import { IonRouterOutlet, IonTabs, ViewDidEnter, ViewDidLeave } from '@ionic/angular';
 import { Subscription } from 'rxjs';
 
 import { CoreUtils } from '@services/utils/utils';
@@ -32,6 +32,7 @@ import { CoreNavBarButtonsComponent } from '../navbar-buttons/navbar-buttons';
 import { StackEvent } from '@ionic/angular/directives/navigation/stack-utils';
 import { CoreNavigator } from '@services/navigator';
 import { CoreTabBase, CoreTabsBaseComponent } from '@classes/tabs';
+import { CoreComponentsRegistry } from '@singletons/components-registry';
 
 /**
  * This component displays some top scrollable tabs that will autohide on vertical scroll.
@@ -70,6 +71,8 @@ export class CoreTabsOutletComponent extends CoreTabsBaseComponent<CoreTabsOutle
 
     constructor(element: ElementRef) {
         super(element);
+
+        CoreComponentsRegistry.register(element.nativeElement, this);
     }
 
     /**
@@ -165,6 +168,15 @@ export class CoreTabsOutletComponent extends CoreTabsBaseComponent<CoreTabsOutle
         this.lastActiveComponent?.ionViewDidLeave?.();
     }
 
+    /**
+     * Get router outlet.
+     *
+     * @returns Router outlet
+     */
+    getOutlet(): IonRouterOutlet {
+        return this.ionTabs.outlet;
+    }
+
     /**
      * Load the tab.
      *
diff --git a/src/core/directives/collapsible-header.ts b/src/core/directives/collapsible-header.ts
index 95c31c943..61c2f9d1a 100644
--- a/src/core/directives/collapsible-header.ts
+++ b/src/core/directives/collapsible-header.ts
@@ -12,336 +12,331 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-import { Directive, ElementRef, OnDestroy } from '@angular/core';
+import { Directive, ElementRef, OnDestroy, OnInit } from '@angular/core';
+import { CoreTabsOutletComponent } from '@components/tabs-outlet/tabs-outlet';
 import { ScrollDetail } from '@ionic/core';
 import { CoreUtils } from '@services/utils/utils';
-import { Platform } from '@singletons';
-import { CoreEventObserver, CoreEvents } from '@singletons/events';
+import { CoreComponentsRegistry } from '@singletons/components-registry';
 import { CoreMath } from '@singletons/math';
+import { Subscription } from 'rxjs';
+import { CoreFormatTextDirective } from './format-text';
 
 /**
- * Directive to make ion-header collapsible.
- * Ion content should have h1 tag inside.
+ * Directive to make <ion-header> collapsible.
+ *
+ * This directive expects h1 titles to be duplicated in a header and an item inside the page, and it will transition
+ * from one state to another listening to the scroll in the page content. The item to be used as the expanded form
+ * should also have the [collapsed] attribute.
  *
  * Example usage:
  *
  * <ion-header collapsible>
+ *     <ion-toolbar>
+ *         <ion-title>
+ *             <h1>Title</h1>
+ *         </ion-title>
+ *     </ion-toolbar>
+ * </ion-header>
+ *
+ * <ion-content>
+ *     <ion-item collapsible>
+ *         <ion-label>
+ *             <h1>Title</h1>
+ *         </ion-label>
+ *     </ion-item>
+ *     ...
+ * </ion-content>
  */
 @Directive({
     selector: 'ion-header[collapsible]',
 })
-export class CoreCollapsibleHeaderDirective implements OnDestroy {
+export class CoreCollapsibleHeaderDirective implements OnInit, OnDestroy {
 
-    protected loadingObserver: CoreEventObserver;
-    protected content?: HTMLIonContentElement | null;
-    protected contentScroll?: HTMLElement;
-    protected header: HTMLIonHeaderElement;
-    protected titleTopDifference = 1;
-    protected h1StartDifference = 0;
-    protected headerH1FontSize = 0;
-    protected contentH1FontSize = 0;
-    protected headerSubHeadingFontSize = 0;
-    protected contentSubHeadingFontSize = 0;
-    protected subHeadingStartDifference = 0;
-    protected inContent = true;
-    protected title?: HTMLElement | null;
-    protected titleHeight = 0;
-    protected contentH1?: HTMLElement | null;
-    protected debouncedUpdateCollapseProgress: () => void;
+    protected page?: HTMLElement;
+    protected collapsedHeader?: Element;
+    protected collapsedFontStyles?: Partial<CSSStyleDeclaration>;
+    protected expandedHeader?: Element;
+    protected expandedHeaderHeight?: number;
+    protected expandedFontStyles?: Partial<CSSStyleDeclaration>;
+    protected content?: HTMLIonContentElement;
+    protected contentScrollListener?: EventListener;
+    protected floatingTitle?: HTMLElement;
+    protected scrollingHeight?: number;
+    protected subscriptions: Subscription[] = [];
 
-    constructor(el: ElementRef<HTMLIonHeaderElement>) {
-        this.header = el.nativeElement;
-        this.debouncedUpdateCollapseProgress = CoreUtils.debounce(() => this.updateCollapseProgress(), 50);
-
-        this.loadingObserver = CoreEvents.on(CoreEvents.CORE_LOADING_CHANGED, async (data) => {
-            if (!data.loaded) {
-                return;
-            }
-
-            const loadingId = await this.getLoadingId();
-            if (loadingId && data.uniqueId == loadingId) {
-                // Remove event when loading is done.
-                this.loadingObserver.off();
-
-                // Wait to render.
-                await CoreUtils.nextTick();
-                this.setupRealTitle();
-            }
-        });
-    }
+    constructor(protected el: ElementRef) {}
 
     /**
-     * Set content element.
-     *
-     * @param content Content element.
+     * @inheritdoc
      */
-    protected async setContent(content?: HTMLIonContentElement | null): Promise<void> {
-        this.content = content;
+    async ngOnInit(): Promise<void> {
+        this.collapsedHeader = this.el.nativeElement;
 
-        if (content) {
-            this.contentScroll = await content.getScrollElement();
-        } else {
-            delete this.contentScroll;
-        }
-    }
+        await Promise.all([
+            this.initializePage(),
+            this.initializeCollapsedHeader(),
+            this.initializeExpandedHeader(),
+        ]);
 
-    /**
-     * Gets the loading content id to wait for the loading to finish.
-     *
-     * @return Promise resolved with Loading Id, if any.
-     */
-    protected async getLoadingId(): Promise<string | undefined> {
-        if (!this.content) {
-            this.setContent(this.header.parentElement?.querySelector('ion-content:not(.disable-scroll-y)'));
-
-            if (!this.content) {
-                this.cannotCollapse();
-
-                return;
-            }
-
-            const title = this.header.parentElement?.querySelector('.collapsible-title') || null;
-
-            if (title) {
-                // Title already found, no need to wait for loading.
-                this.loadingObserver.off();
-                this.setupRealTitle();
-
-                return;
-            }
-
-        }
-
-        return this.content.querySelector('core-loading.core-loading-loaded:not(.core-loading-inline) .core-loading-content')?.id;
-    }
-
-    /**
-     * Call this function when header is not collapsible.
-     */
-    protected cannotCollapse(): void {
-        this.setContent();
-        this.loadingObserver.off();
-        this.header.classList.add('core-header-collapsed');
-    }
-
-    /**
-     * Gets the real title on ion content to watch scroll.
-     *
-     * @return Promise resolved when done.
-     */
-    protected async setupRealTitle(): Promise<void> {
-        if (!this.content) {
-            this.cannotCollapse();
-
-            return;
-        }
-
-        // Wait animations to finish.
-        const animations = (this.content.getAnimations && this.content.getAnimations()) || [];
-        await Promise.all(animations.map(async (animation) => {
-            await animation.finished;
-        }));
-
-        let title = this.content.querySelector<HTMLElement>('.collapsible-title');
-        if (!title) {
-            // Title is outside the ion-content.
-            title = this.header.parentElement?.querySelector('.collapsible-title') || null;
-            this.inContent = false;
-        }
-        this.contentH1 = title?.querySelector<HTMLElement>('h1');
-        const headerH1 = this.header.querySelector<HTMLElement>('h1');
-        if (!title || !this.contentH1 || !headerH1 || !this.contentH1.parentElement) {
-            this.cannotCollapse();
-
-            return;
-        }
-
-        this.title = title;
-        this.titleHeight = title.getBoundingClientRect().height;
-        this.titleTopDifference = this.contentH1.getBoundingClientRect().top - headerH1.getBoundingClientRect().top;
-
-        if (this.titleTopDifference <= 0) {
-            this.cannotCollapse();
-
-            return;
-        }
-
-        // Split view part.
-        const contentAux = this.header.parentElement?.querySelector<HTMLElement>('ion-content.disable-scroll-y');
-        if (contentAux) {
-            if (contentAux.querySelector('core-split-view.menu-and-content')) {
-                this.cannotCollapse();
-                title.remove();
-
-                return;
-            }
-            contentAux.style.setProperty('--offset-top', this.header.clientHeight + 'px');
-        }
-
-        const headerH1Styles = getComputedStyle(headerH1);
-        const contentH1Styles = getComputedStyle(this.contentH1);
-
-        if (Platform.isRTL) {
-            // Checking position over parent because transition may not be finished.
-            const contentH1Position = this.contentH1.getBoundingClientRect().right - this.content.getBoundingClientRect().right;
-            const headerH1Position = headerH1.getBoundingClientRect().right - this.header.getBoundingClientRect().right;
-
-            this.h1StartDifference = Math.round(contentH1Position - (headerH1Position - parseFloat(headerH1Styles.paddingRight)));
-        } else {
-            // Checking position over parent because transition may not be finished.
-            const contentH1Position = this.contentH1.getBoundingClientRect().left - this.content.getBoundingClientRect().left;
-            const headerH1Position = headerH1.getBoundingClientRect().left - this.header.getBoundingClientRect().left;
-
-            this.h1StartDifference = Math.round(contentH1Position - (headerH1Position + parseFloat(headerH1Styles.paddingLeft)));
-        }
-
-        this.headerH1FontSize = parseFloat(headerH1Styles.fontSize);
-        this.contentH1FontSize = parseFloat(contentH1Styles.fontSize);
-
-        // Transfer font styles.
-        Array.from(headerH1Styles).forEach((styleName) => {
-            if (styleName != 'font-size' &&
-                styleName != 'font-family' &&
-                (styleName.startsWith('font-') || styleName.startsWith('letter-'))) {
-                this.contentH1?.style.setProperty(styleName, headerH1Styles.getPropertyValue(styleName));
-            }
-        });
-        this.contentH1.style.setProperty(
-            '--max-width',
-            (parseFloat(headerH1Styles.width)
-                -parseFloat(headerH1Styles.paddingLeft)
-                -parseFloat(headerH1Styles.paddingRight)
-                +'px'),
-        );
-
-        this.contentH1.setAttribute('aria-hidden', 'true');
-
-        // Clone element to let the other elements be static.
-        const contentH1Clone = this.contentH1.cloneNode(true) as HTMLElement;
-        contentH1Clone.classList.add('cloned');
-        this.contentH1.parentElement.insertBefore(contentH1Clone, this.contentH1);
-        this.contentH1.style.setProperty(
-            'top',
-            (contentH1Clone.getBoundingClientRect().top -
-            this.contentH1.parentElement.getBoundingClientRect().top +
-            parseInt(getComputedStyle(this.contentH1.parentElement).marginTop || '0', 10)) + 'px',
-        );
-        this.contentH1.style.setProperty('position', 'absolute');
-        this.contentH1.parentElement.style.setProperty('position', 'relative');
-
-        this.setupContent();
-    }
-
-    /**
-     * Setup content scroll.
-     *
-     * @param parentId Parent id to recalculate content
-     * @param retries  Retries to find content in case it's loading.
-     */
-    async setupContent(parentId?: string, retries = 5): Promise<void> {
-        if (parentId) {
-            this.setContent(this.header.parentElement?.querySelector(`#${parentId} ion-content:not(.disable-scroll-y)`));
-            this.inContent = false;
-            if (!this.content && retries > 0) {
-                await CoreUtils.nextTick();
-                await this.setupContent(parentId, --retries);
-
-                return;
-            }
-
-            this.updateCollapseProgress();
-        }
-
-        if (!this.title || !this.content) {
-            return;
-        }
-
-        // Add something under the hood to change the page background.
-        let color = getComputedStyle(this.title).getPropertyValue('backgroundColor').trim();
-        if (color == '') {
-            color = getComputedStyle(this.title).getPropertyValue('--background').trim();
-        }
-
-        const underHeader = document.createElement('div');
-        underHeader.classList.add('core-underheader');
-        underHeader.style.setProperty('height', this.header.clientHeight + 'px');
-        underHeader.style.setProperty('background', color);
-        if (this.inContent) {
-            this.content.shadowRoot?.querySelector('#background-content')?.prepend(underHeader);
-            this.content.style.setProperty('--offset-top', this.header.clientHeight + 'px');
-        } else {
-            if (!this.header.closest('.ion-page')?.querySelector('.core-underheader')) {
-                this.header.closest('.ion-page')?.insertBefore(underHeader, this.header);
-            }
-        }
-
-        this.content.scrollEvents = true;
-        this.content.addEventListener('ionScroll', ({ target }: CustomEvent<ScrollDetail>): void => {
-            if (target !== this.content) {
-                return;
-            }
-
-            this.updateCollapseProgress();
-            this.debouncedUpdateCollapseProgress();
-        });
-    }
-
-    /**
-     * Update collapse progress according to the current scroll position.
-     */
-    protected updateCollapseProgress(): void {
-        if (!this.contentScroll || !this.title || !this.contentH1) {
-            return;
-        }
-
-        const collapsibleHeaderHeight = this.title.shadowRoot?.children[0].clientHeight ?? this.title.clientHeight;
-        const scrollableHeight = this.contentScroll.scrollHeight - this.contentScroll.clientHeight;
-        const collapsedHeight = collapsibleHeaderHeight - this.title.clientHeight;
-        let progress = 0;
-        if (scrollableHeight !== 0) {
-            progress = CoreMath.clamp(
-                scrollableHeight + collapsedHeight <= 2 * collapsibleHeaderHeight
-                    ? this.contentScroll.scrollTop / scrollableHeight
-                    : this.contentScroll.scrollTop / collapsibleHeaderHeight,
-                0,
-                1,
-            );
-        }
-        const collapsed = progress === 1;
-
-        if (!this.inContent) {
-            this.title.style.transform = `translateY(-${this.titleTopDifference * progress}px)`;
-            this.title.style.height = `${collapsibleHeaderHeight * (1 - progress)}px`;
-        }
-
-        // Check total collapse.
-        this.header.classList.toggle('core-header-collapsed', collapsed);
-        this.title.classList.toggle('collapsible-title-collapsed', collapsed);
-        this.title.classList.toggle('collapsible-title-collapse-started', progress > 0);
-        this.title.classList.toggle('collapsible-title-collapse-nowrap', progress > 0.5);
-        this.title.style.setProperty('--collapse-opacity', `${1 - progress}`);
-
-        if (collapsed) {
-            this.contentH1.style.transform = `translateX(-${this.h1StartDifference}px)`;
-            this.contentH1.style.setProperty('font-size', `${this.headerH1FontSize}px`);
-
-            return;
-        }
-
-        // Zoom font-size out.
-        const newFontSize = this.contentH1FontSize - ((this.contentH1FontSize - this.headerH1FontSize) * progress);
-        this.contentH1.style.setProperty('font-size', `${newFontSize}px`);
-
-        // Move.
-        const newStart = -this.h1StartDifference * progress;
-        this.contentH1.style.transform = `translateX(${newStart}px)`;
+        this.initializeFloatingTitle();
+        this.initializeContent();
     }
 
     /**
      * @inheritdoc
      */
     ngOnDestroy(): void {
-        this.loadingObserver.off();
+        this.subscriptions.forEach(subscription => subscription.unsubscribe());
+
+        if (this.content && this.contentScrollListener) {
+            this.content.removeEventListener('ionScroll', this.contentScrollListener);
+        }
+    }
+
+    /**
+     * Search the page element, initialize it, and wait until it's ready for the transition to trigger on scroll.
+     */
+    protected async initializePage(): Promise<void> {
+        if (!this.collapsedHeader?.parentElement) {
+            throw new Error('[collapsible-header] Couldn\'t get page');
+        }
+
+        // Find element and prepare classes.
+        this.page = this.collapsedHeader.parentElement;
+
+        this.page.classList.add('collapsible-header-page');
+    }
+
+    /**
+     * Search the collapsed header element, initialize it, and wait until it's ready for the transition to trigger on scroll.
+     */
+    protected async initializeCollapsedHeader(): Promise<void> {
+        if (!this.collapsedHeader) {
+            throw new Error('[collapsible-header] Couldn\'t initialize collapsed header');
+        }
+
+        this.collapsedHeader.classList.add('collapsible-header-collapsed');
+
+        await this.waitFormatTextsRendered(this.collapsedHeader);
+    }
+
+    /**
+     * Search the expanded header element, initialize it, and wait until it's ready for the transition to trigger on scroll.
+     */
+    protected async initializeExpandedHeader(): Promise<void> {
+        do {
+            await CoreUtils.wait(50);
+
+            this.expandedHeader = this.page?.querySelector('ion-item[collapsible]') ?? undefined;
+
+            if (!this.expandedHeader) {
+                continue;
+            }
+
+            await this.waitFormatTextsRendered(this.expandedHeader);
+        } while (
+            !this.expandedHeader ||
+            this.expandedHeader.clientHeight === 0 ||
+            this.expandedHeader.closest('ion-content.animating')
+        );
+
+        this.expandedHeader.classList.add('collapsible-header-expanded');
+    }
+
+    /**
+     * Search the page content, initialize it, and wait until it's ready for the transition to trigger on scroll.
+     */
+    protected async initializeContent(): Promise<void> {
+        // Initialize from tabs.
+        const tabs = CoreComponentsRegistry.resolve(this.page?.querySelector('core-tabs-outlet'), CoreTabsOutletComponent);
+
+        if (tabs) {
+            const outlet = tabs.getOutlet();
+            const onOutletUpdated = () => {
+                const activePage = outlet.nativeEl.querySelector('.ion-page:not(.ion-page-hidden)');
+
+                this.updateContent(activePage?.querySelector('ion-content:not(.disable-scroll-y)') as HTMLIonContentElement);
+            };
+
+            this.subscriptions.push(outlet.activateEvents.subscribe(onOutletUpdated));
+            this.subscriptions.push(outlet.deactivateEvents.subscribe(onOutletUpdated));
+
+            onOutletUpdated();
+
+            return;
+        }
+
+        // Initialize from page content.
+        const content = this.page?.querySelector('ion-content:not(.disable-scroll-y)');
+
+        if (!content) {
+            throw new Error('[collapsible-header] Couldn\'t get content');
+        }
+
+        this.trackContentScroll(content as HTMLIonContentElement);
+    }
+
+    /**
+     * Initialize a floating title to mimic transitioning the title from one state to the other.
+     */
+    protected initializeFloatingTitle(): void {
+        if (!this.page || !this.collapsedHeader || !this.expandedHeader) {
+            throw new Error('[collapsible-header] Couldn\'t create floating title');
+        }
+
+        // Add floating title and measure initial position.
+        const collapsedHeaderTitle = this.collapsedHeader.querySelector('h1') as HTMLElement;
+        const originalTitle = this.expandedHeader.querySelector('h1') as HTMLElement;
+        const floatingTitleWrapper = originalTitle.parentElement as HTMLElement;
+        const floatingTitle = originalTitle.cloneNode(true) as HTMLElement;
+
+        originalTitle.classList.add('collapsible-header-original-title');
+        floatingTitle.classList.add('collapsible-header-floating-title');
+        floatingTitleWrapper.classList.add('collapsible-header-floating-title-wrapper');
+        floatingTitleWrapper.insertBefore(floatingTitle, originalTitle);
+
+        const floatingTitleBoundingBox = floatingTitle.getBoundingClientRect();
+
+        // Prepare styles variables.
+        const collapsedHeaderTitleBoundingBox = collapsedHeaderTitle.getBoundingClientRect();
+        const collapsedTitleStyles = getComputedStyle(collapsedHeaderTitle);
+        const expandedHeaderHeight = this.expandedHeader.clientHeight;
+        const expandedTitleStyles = getComputedStyle(originalTitle);
+        const originalTitleBoundingBox = originalTitle.getBoundingClientRect();
+        const textProperties = ['overflow', 'white-space', 'text-overflow', 'color'];
+        const [collapsedFontStyles, expandedFontStyles] = Array
+            .from(collapsedTitleStyles)
+            .filter(
+                property =>
+                    property.startsWith('font-') ||
+                    property.startsWith('letter-') ||
+                    textProperties.includes(property),
+            )
+            .reduce((styles, property) => {
+                styles[0][property] = collapsedTitleStyles.getPropertyValue(property);
+                styles[1][property] = expandedTitleStyles.getPropertyValue(property);
+
+                return styles;
+            }, [{}, {}]);
+        const cssVariables = {
+            '--collapsible-header-collapsed-height': `${this.collapsedHeader.clientHeight}px`,
+            '--collapsible-header-expanded-y-delta': `-${this.collapsedHeader.clientHeight}px`,
+            '--collapsible-header-expanded-height': `${expandedHeaderHeight}px`,
+            '--collapsible-header-floating-title-top': `${originalTitleBoundingBox.top - floatingTitleBoundingBox.top}px`,
+            '--collapsible-header-floating-title-left': `${originalTitleBoundingBox.left - floatingTitleBoundingBox.left}px`,
+            '--collapsible-header-floating-title-width': `${originalTitle.clientWidth}px`,
+            '--collapsible-header-floating-title-x-delta':
+                `${collapsedHeaderTitleBoundingBox.left - originalTitleBoundingBox.left}px`,
+            '--collapsible-header-floating-title-width-delta': `${collapsedHeaderTitle.clientWidth - originalTitle.clientWidth}px`,
+        };
+
+        Object
+            .entries(cssVariables)
+            .forEach(([property, value]) => this.page?.style.setProperty(property, value));
+
+        Object
+            .entries(expandedFontStyles)
+            .forEach(([property, value]) => floatingTitle.style.setProperty(property, value as string));
+
+        // Activate styles.
+        this.page.classList.add('is-active');
+
+        this.floatingTitle = floatingTitle;
+        this.scrollingHeight = originalTitleBoundingBox.top - collapsedHeaderTitleBoundingBox.top;
+        this.collapsedFontStyles = collapsedFontStyles;
+        this.expandedFontStyles = expandedFontStyles;
+        this.expandedHeaderHeight = expandedHeaderHeight;
+    }
+
+    /**
+     * Wait until all <core-format-text> children inside the element are done rendering.
+     *
+     * @param element Element.
+     */
+    protected async waitFormatTextsRendered(element: Element): Promise<void> {
+        const formatTexts = Array
+            .from(element.querySelectorAll('core-format-text'))
+            .map(element => CoreComponentsRegistry.resolve(element, CoreFormatTextDirective));
+
+        await Promise.all(formatTexts.map(formatText => formatText?.rendered()));
+    }
+
+    /**
+     * Update content element whos scroll is being tracked.
+     *
+     * @param content Content element.
+     */
+    protected updateContent(content?: HTMLIonContentElement | null): void {
+        if (this.content && this.contentScrollListener) {
+            this.content.removeEventListener('ionScroll', this.contentScrollListener);
+
+            delete this.content;
+            delete this.contentScrollListener;
+        }
+
+        content && this.trackContentScroll(content);
+    }
+
+    /**
+     * Listen to a content element for scroll events that will control the header state transition.
+     *
+     * @param content Content element.
+     */
+    protected async trackContentScroll(content: HTMLIonContentElement): Promise<void> {
+        if (content === this.content) {
+            return;
+        }
+
+        const page = this.page;
+        const scrollingHeight = this.scrollingHeight;
+        const expandedHeader = this.expandedHeader;
+        const expandedHeaderHeight = this.expandedHeaderHeight;
+        const expandedFontStyles = this.expandedFontStyles;
+        const collapsedFontStyles = this.collapsedFontStyles;
+        const floatingTitle = this.floatingTitle;
+        const contentScroll = await content.getScrollElement();
+
+        if (
+            !page ||
+            !scrollingHeight ||
+            !expandedHeader ||
+            !expandedHeaderHeight ||
+            !expandedFontStyles ||
+            !collapsedFontStyles ||
+            !floatingTitle
+        ) {
+            throw new Error('[collapsible-header] Couldn\'t set up scrolling');
+        }
+
+        page.style.setProperty('--collapsible-header-progress', '0');
+        page.classList.toggle('is-within-content', content.contains(expandedHeader));
+        page.classList.toggle('is-collapsed', false);
+
+        Object
+            .entries(expandedFontStyles)
+            .forEach(([property, value]) => floatingTitle.style.setProperty(property, value as string));
+
+        this.content = content;
+        this.content.addEventListener('ionScroll', this.contentScrollListener = ({ target }: CustomEvent<ScrollDetail>): void => {
+            if (target !== this.content) {
+                return;
+            }
+
+            const scrollableHeight = contentScroll.scrollHeight - contentScroll.clientHeight;
+            const collapsedHeight = expandedHeaderHeight - (expandedHeader.clientHeight ?? 0);
+            const frozen = scrollableHeight + collapsedHeight <= 2 * expandedHeaderHeight;
+            const progress = frozen
+                ? 0
+                :  CoreMath.clamp(contentScroll.scrollTop / scrollingHeight, 0, 1);
+
+            page.style.setProperty('--collapsible-header-progress', `${progress}`);
+            page.classList.toggle('is-frozen', frozen);
+            page.classList.toggle('is-collapsed', progress === 1);
+
+            Object
+                .entries(progress > .5 ? collapsedFontStyles : expandedFontStyles)
+                .forEach(([property, value]) => floatingTitle.style.setProperty(property, value as string));
+        });
     }
 
 }
diff --git a/src/core/directives/format-text.ts b/src/core/directives/format-text.ts
index 959735eef..5171ae54b 100644
--- a/src/core/directives/format-text.ts
+++ b/src/core/directives/format-text.ts
@@ -39,6 +39,7 @@ import { CoreFilter, CoreFilterFilter, CoreFilterFormatTextOptions } from '@feat
 import { CoreFilterDelegate } from '@features/filter/services/filter-delegate';
 import { CoreFilterHelper } from '@features/filter/services/filter-helper';
 import { CoreSubscriptions } from '@singletons/subscriptions';
+import { CoreComponentsRegistry } from '@singletons/components-registry';
 
 /**
  * Directive to format text rendered. It renders the HTML and treats all links and media, using CoreLinkDirective
@@ -95,6 +96,8 @@ export class CoreFormatTextDirective implements OnChanges {
         @Optional() protected content: IonContent,
         protected viewContainerRef: ViewContainerRef,
     ) {
+        CoreComponentsRegistry.register(element.nativeElement, this);
+
         this.element = element.nativeElement;
         this.element.classList.add('core-format-text-loading'); // Hide contents until they're treated.
 
@@ -125,6 +128,22 @@ export class CoreFormatTextDirective implements OnChanges {
         }
     }
 
+    /**
+     * Wait until the text is fully rendered.
+     */
+    async rendered(): Promise<void> {
+        if (!this.element.classList.contains('core-format-text-loading')) {
+            return;
+        }
+
+        await new Promise<void>(resolve => {
+            const subscription = this.afterRender.subscribe(() => {
+                subscription.unsubscribe();
+                resolve();
+            });
+        });
+    }
+
     /**
      * Apply CoreExternalContentDirective to a certain element.
      *
diff --git a/src/core/features/course/components/module-info/core-course-module-info.html b/src/core/features/course/components/module-info/core-course-module-info.html
index f6f50dd35..a4e77744e 100644
--- a/src/core/features/course/components/module-info/core-course-module-info.html
+++ b/src/core/features/course/components/module-info/core-course-module-info.html
@@ -1,4 +1,4 @@
-<ion-item class="ion-text-wrap collapsible-title">
+<ion-item class="ion-text-wrap" collapsible>
     <core-mod-icon slot="start" [modicon]="modicon" [modname]="module.modname" [componentId]="module.instance">
     </core-mod-icon>
     <ion-label>
diff --git a/src/core/features/course/components/module-summary/module-summary.scss b/src/core/features/course/components/module-summary/module-summary.scss
index 59ce443d5..5f86396c2 100644
--- a/src/core/features/course/components/module-summary/module-summary.scss
+++ b/src/core/features/course/components/module-summary/module-summary.scss
@@ -1,6 +1,6 @@
 @import "~theme/globals";
 
-:host ::ng-deep .collapsible-title ion-label {
+:host ::ng-deep ion-item[collapsible] ion-label {
     margin-top: 12px;
 }
 
diff --git a/src/core/features/course/format/singleactivity/components/single-activity.scss b/src/core/features/course/format/singleactivity/components/single-activity.scss
index 1352a5254..50ff5bd01 100644
--- a/src/core/features/course/format/singleactivity/components/single-activity.scss
+++ b/src/core/features/course/format/singleactivity/components/single-activity.scss
@@ -1,3 +1,3 @@
-:host ::ng-deep .collapsible-title {
+:host ::ng-deep ion-item[collapsible] {
     display: none;
 }
diff --git a/src/core/features/course/pages/index/index.html b/src/core/features/course/pages/index/index.html
index 2a234b5d5..c1d586d11 100644
--- a/src/core/features/course/pages/index/index.html
+++ b/src/core/features/course/pages/index/index.html
@@ -16,7 +16,7 @@
         </ion-buttons>
     </ion-toolbar>
 </ion-header>
-<ion-item class="core-format-progress-list ion-text-wrap collapsible-title list-item-limited-width">
+<ion-item class="core-format-progress-list ion-text-wrap list-item-limited-width" collapsible>
     <ion-avatar slot="start" class="core-course-thumb" *ngIf="imageThumb">
         <img [src]="imageThumb" core-external-content alt="" />
     </ion-avatar>
@@ -29,4 +29,4 @@
     </ion-label>
 
 </ion-item>
-<core-tabs-outlet [tabs]="tabs" [hideUntil]="loaded" (ionChange)="tabSelected($event)"></core-tabs-outlet>
+<core-tabs-outlet [tabs]="tabs" [hideUntil]="loaded" (ionChange)="tabSelected()"></core-tabs-outlet>
diff --git a/src/core/features/course/pages/index/index.ts b/src/core/features/course/pages/index/index.ts
index c6b24df14..82ddef122 100644
--- a/src/core/features/course/pages/index/index.ts
+++ b/src/core/features/course/pages/index/index.ts
@@ -171,9 +171,7 @@ export class CoreCourseIndexPage implements OnInit, OnDestroy {
     /**
      * A tab was selected.
      */
-    tabSelected(tabToSelect: CoreTabsOutletTab): void {
-        this.ionCollapsibleHeader?.setupContent(tabToSelect.id);
-
+    tabSelected(): void {
         if (!this.module || !this.course) {
             return;
         }
diff --git a/src/core/singletons/components-registry.ts b/src/core/singletons/components-registry.ts
new file mode 100644
index 000000000..a5c7b12fb
--- /dev/null
+++ b/src/core/singletons/components-registry.ts
@@ -0,0 +1,53 @@
+// (C) Copyright 2015 Moodle Pty Ltd.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+/**
+ * Registry to keep track of component instances.
+ */
+export class CoreComponentsRegistry {
+
+    private static instances: WeakMap<Element, unknown> = new WeakMap();
+
+    /**
+     * Register a component instance.
+     *
+     * @param element Root element.
+     * @param instance Component instance.
+     */
+    static register(element: Element, instance: unknown): void {
+        this.instances.set(element, instance);
+    }
+
+    /**
+     * Resolve a component instance.
+     *
+     * @param element Root element.
+     * @param componentClass Component class.
+     * @returns Component instance.
+     */
+    static resolve<T>(element?: Element | null, componentClass?: ComponentConstructor<T>): T | null {
+        const instance = (element && this.instances.get(element) as T) ?? null;
+
+        return instance && (!componentClass || instance instanceof componentClass)
+            ? instance
+            : null;
+    }
+
+}
+
+/**
+ * Component constructor.
+ */
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+export type ComponentConstructor<T> = { new(...args: any[]): T };
diff --git a/src/theme/components/collapsible-header.scss b/src/theme/components/collapsible-header.scss
new file mode 100644
index 000000000..750a3807f
--- /dev/null
+++ b/src/theme/components/collapsible-header.scss
@@ -0,0 +1,86 @@
+.collapsible-header-page {
+    --collapsible-header-progress: 0;
+    --collapsible-header-collapsed-height: 0px;
+    --collapsible-header-expanded-y-delta: 0px;
+    --collapsible-header-expanded-height: 0px;
+    --collapsible-header-floating-title-top: 0px;
+    --collapsible-header-floating-title-left: 0px;
+    --collapsible-header-floating-title-width: 0px;
+    --collapsible-header-floating-title-x-delta: 0px;
+    --collapsible-header-floating-title-width-delta: 0px;
+
+    .collapsible-header-expanded .collapsible-header-floating-title {
+        position: absolute;
+        top: var(--collapsible-header-floating-title-top);
+        left: var(--collapsible-header-floating-title-left);
+        transform: translateX(calc(var(--collapsible-header-floating-title-x-delta) * var(--collapsible-header-progress)));
+        opacity: 0;
+    }
+
+    &:not(.is-collapsed) .collapsible-header-collapsed {
+        --core-header-toolbar-border-width: 0;
+        --core-header-toolbar-background: transparent;
+
+        h1 {
+            opacity: 0;
+        }
+
+    }
+
+    &.is-active {
+
+        .collapsible-header-expanded {
+            height: calc(var(--collapsible-header-expanded-height) * (1 - var(--collapsible-header-progress)));
+            transform: translateY(calc(var(--collapsible-header-expanded-y-delta) * var(--collapsible-header-progress)));
+            overflow: visible;
+
+            @include core-transition(height transform, 200ms, linear);
+
+            .collapsible-header-floating-title {
+                opacity: 1;
+                width: calc(var(--collapsible-header-floating-title-width) + var(--collapsible-header-progress) * var(--collapsible-header-floating-title-width-delta));
+
+                @include core-transition(width transform, 200ms, linear);
+            }
+
+            .collapsible-header-original-title {
+                opacity: 0;
+            }
+
+            & > *:not(.collapsible-header-floating-title-wrapper),
+            .collapsible-header-floating-title-wrapper > *:not(.collapsible-header-floating-title):not(.collapsible-header-original-title) {
+                opacity: calc(1 - var(--collapsible-header-progress));
+
+                @include core-transition(opacity, 200ms, linear);
+            }
+
+        }
+
+    }
+
+    &.is-active.is-within-content  {
+
+        ion-content {
+            --offset-top: var(--collapsible-header-collapsed-height) !important;
+        }
+
+        .collapsible-header-expanded {
+            transform: none;
+            height: auto;
+        }
+
+    }
+
+    &.is-active.is-frozen {
+
+        .collapsible-header-floating-title {
+            display: none;
+        }
+
+        .collapsible-header-expanded h1 {
+            opacity: 1;
+        }
+
+    }
+
+}
diff --git a/src/theme/globals.mixins.scss b/src/theme/globals.mixins.scss
index 2199bf76b..e77e74181 100644
--- a/src/theme/globals.mixins.scss
+++ b/src/theme/globals.mixins.scss
@@ -25,12 +25,17 @@
     // border: var(--a11y-focus-width) solid var(--a11y-focus-color);
 }
 
-@mixin core-transition($property: all, $duration: 500ms, $timing-function: ease-in-out) {
-    -webkit-transition: $property $duration $timing-function;
-    -moz-transition: $property $duration $timing-function;
-    -ms-transition: $property $duration $timing-function;
-    -o-transition: $property $duration $timing-function;
-    transition: $property $duration $timing-function;
+@mixin core-transition($properties: all, $duration: 500ms, $timing-function: ease-in-out) {
+    $transitions: ();
+    @each $property in $properties {
+      $transitions: append($transitions, $property $duration $timing-function, comma);
+    }
+
+    -webkit-transition: $transitions;
+    -moz-transition: $transitions;
+    -ms-transition: $transitions;
+    -o-transition: $transitions;
+    transition: $transitions;
 }
 
 @mixin push-arrow-color($color: dedede, $flip-rtl: false) {
diff --git a/src/theme/theme.base.scss b/src/theme/theme.base.scss
index 9a182fa5c..2c79ec6b5 100644
--- a/src/theme/theme.base.scss
+++ b/src/theme/theme.base.scss
@@ -1487,89 +1487,7 @@ ion-header.no-title {
     }
 }
 
-ion-header[collapsible] {
-    @include core-transition(all, 500ms);
 
-    ion-title {
-        @include core-transition(opacity, 0ms);
-    }
-}
-
-// Only hide header when not in fullscreen.
-body:not(.core-iframe-fullscreen) ion-header[collapsible]:not(.core-header-collapsed) {
-    ion-toolbar {
-        --core-header-toolbar-background: rgba(255, 255, 255, 0);
-        --core-header-toolbar-border-width: 0;
-    }
-
-    ion-title, &::after {
-        opacity: 0;
-        z-index: 0;
-    }
-}
-
-.collapsible-title {
-    overflow: visible;
-    --inner-padding-top: 0px;
-    --padding-top: 0px;
-
-    ion-label {
-        margin-top: 0px;
-    }
-
-    *, h1 {
-        @include core-transition(all, 200ms, linear);
-    }
-
-    ion-label {
-        overflow: visible !important;
-    }
-
-    h1 {
-        --max-width: none;
-    }
-    h1.cloned {
-        opacity: 0 !important;
-    }
-}
-
-ion-app.ios .collapsible-title h1 {
-    font-weight: 600; // Default heading weight.
-}
-ion-app.md .collapsible-title h1 {
-    font-weight: 500; // Default heading weight.
-    letter-spacing: .0125em;
-}
-
-.collapsible-title.collapsible-title-collapsed {
-    ion-label, h1, ion-row, ion-col {
-        opacity: 0;
-    }
-}
-
-.collapsible-title.collapsible-title-collapse-started {
-    * {
-        opacity: var(--collapse-opacity, 0);
-    }
-
-    ion-label, h1, ion-row, ion-col, .subheading {
-        opacity: 1;
-    }
-}
-
-.collapsible-title.collapsible-title-collapse-nowrap {
-    h1:not(.cloned) {
-        max-width: var(--max-width);
-        white-space: nowrap;
-        overflow: hidden;
-        text-overflow: ellipsis;
-    }
-}
-
-// In fullscreen, disable the offset-top added by collapsible header.
-body.core-iframe-fullscreen ion-content {
-    --offset-top: 0px !important;
-}
 
 // To make core-swipe-slides fill the remaining height.
 .core-swipe-slides-container {
diff --git a/src/theme/theme.scss b/src/theme/theme.scss
index 385b314f6..cd0769b6d 100644
--- a/src/theme/theme.scss
+++ b/src/theme/theme.scss
@@ -19,6 +19,7 @@
 @import "./theme.base.scss";
 
 /* Components */
+@import "./components/collapsible-header.scss";
 @import "./components/format-text.scss";
 @import "./components/rubrics.scss";
 @import "./components/mod-label.scss";