diff --git a/package-lock.json b/package-lock.json
index 68badf40816..ba181e2bbfb 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -137,6 +137,7 @@
         "rimraf": "^6.1.2",
         "rollup": "^4.54.0",
         "rollup-plugin-clear": "^2.0.7",
+        "shadow-dom-testing-library": "^1.13.1",
         "storage-mock": "^2.1.0",
         "storybook": "10.1.11",
         "stylelint": "^16.26.1",
@@ -28955,6 +28956,20 @@
       "integrity": "sha512-E5LDX7Wrp85Kil5bhZv46j8jOeboKq5JMmYM3gVGdGH8xFpPWXUMsNrlODCrkoxMEeNi/XZIwuRvY4XNwYMJpw==",
       "dev": true
     },
+    "node_modules/shadow-dom-testing-library": {
+      "version": "1.13.1",
+      "resolved": "https://registry.npmjs.org/shadow-dom-testing-library/-/shadow-dom-testing-library-1.13.1.tgz",
+      "integrity": "sha512-X73VDI3KumYeYuz/C2yjn4/1bsUN68JleYI3NwFJUDa+5fWhO//s+02gdxdetY+mVRYZosVokkkmIhdzjABnmQ==",
+      "dev": true,
+      "license": "MIT",
+      "engines": {
+        "node": ">= 14",
+        "npm": ">= 7"
+      },
+      "peerDependencies": {
+        "@testing-library/dom": ">= 8"
+      }
+    },
     "node_modules/shallow-clone": {
       "version": "3.0.1",
       "resolved": "https://registry.npmjs.org/shallow-clone/-/shallow-clone-3.0.1.tgz",
@@ -53551,6 +53566,12 @@
       "integrity": "sha512-E5LDX7Wrp85Kil5bhZv46j8jOeboKq5JMmYM3gVGdGH8xFpPWXUMsNrlODCrkoxMEeNi/XZIwuRvY4XNwYMJpw==",
       "dev": true
     },
+    "shadow-dom-testing-library": {
+      "version": "1.13.1",
+      "resolved": "https://registry.npmjs.org/shadow-dom-testing-library/-/shadow-dom-testing-library-1.13.1.tgz",
+      "integrity": "sha512-X73VDI3KumYeYuz/C2yjn4/1bsUN68JleYI3NwFJUDa+5fWhO//s+02gdxdetY+mVRYZosVokkkmIhdzjABnmQ==",
+      "dev": true
+    },
     "shallow-clone": {
       "version": "3.0.1",
       "resolved": "https://registry.npmjs.org/shallow-clone/-/shallow-clone-3.0.1.tgz",
diff --git a/package.json b/package.json
index 1eb5637ae43..6c67ee7b1f0 100644
--- a/package.json
+++ b/package.json
@@ -166,6 +166,7 @@
     "rimraf": "^6.1.2",
     "rollup": "^4.54.0",
     "rollup-plugin-clear": "^2.0.7",
+    "shadow-dom-testing-library": "^1.13.1",
     "storage-mock": "^2.1.0",
     "storybook": "10.1.11",
     "stylelint": "^16.26.1",
diff --git a/src/collapse/collapse-content.tsx b/src/collapse/collapse-content.tsx
index a087ec2b13e..da691d2e3c3 100644
--- a/src/collapse/collapse-content.tsx
+++ b/src/collapse/collapse-content.tsx
@@ -2,7 +2,6 @@ import React, {useState, useEffect, useRef, useContext, type PropsWithChildren}
 import classNames from 'classnames';
 
 import dataTests from '../global/data-tests';
-import {getRect} from '../global/dom';
 import {toPx} from './utils';
 import CollapseContext from './collapse-context';
 import {COLLAPSE_CONTENT_TEST_ID, COLLAPSE_CONTENT_CONTAINER_TEST_ID} from './consts';
@@ -60,13 +59,19 @@ export const CollapseContent: React.FC<PropsWithChildren<Props>> = ({
   }
 
   useEffect(() => {
-    if (contentRef.current) {
-      const observer = new ResizeObserver(() => {
-        setContentHeight(getRect(contentRef.current).height);
-      });
+    const observer = new ResizeObserver(([entry]) => {
+      if (entry.target.isConnected) {
+        setContentHeight(entry.contentRect.height);
+      }
+    });
 
+    if (contentRef.current) {
       observer.observe(contentRef.current);
     }
+
+    return () => {
+      observer.disconnect();
+    };
   }, []);
 
   const calculatedDuration = duration + contentHeight * DURATION_FACTOR;
diff --git a/src/collapse/collapse.stories.tsx b/src/collapse/collapse.stories.tsx
index 34af304be11..bc34d4b5025 100644
--- a/src/collapse/collapse.stories.tsx
+++ b/src/collapse/collapse.stories.tsx
@@ -7,6 +7,7 @@ import LoaderInline from '../loader-inline/loader-inline';
 import Collapse from './collapse';
 import CollapseContent from './collapse-content';
 import CollapseControl from './collapse-control';
+import {createShadowRootStyleSheet, ShadowRootWrap} from './shadow-root-test-helpers';
 
 import styles from './collapse.stories.css';
 
@@ -84,11 +85,11 @@ export const WithIcon = () => (
     <Collapse>
       <CollapseControl>
         {(collapsed: boolean) =>
-          (collapsed ? (
+          collapsed ? (
             <Button aria-label='Expand' icon={ChevronDownIcon} className={styles.check} />
           ) : (
             <Button aria-label='Collapse' icon={ChevronUpIcon} className={styles.check} />
-          ))
+          )
         }
       </CollapseControl>
       <CollapseContent>{text}</CollapseContent>
@@ -202,3 +203,15 @@ WithControlledCollapseState.storyName = 'With controlled collapse state';
 WithControlledCollapseState.parameters = {
   screenshots: {actions: [{type: 'click', selector: '[data-test~=trigger]'}]},
 };
+
+export const WrappedInShadowRoot = () => {
+  const styleSheet = createShadowRootStyleSheet(['.container', '.transition', '.summary', '.trigger', '.fade']);
+
+  return (
+    <ShadowRootWrap adoptedStyleSheets={[styleSheet]}>
+      <Basic />
+    </ShadowRootWrap>
+  );
+};
+
+WrappedInShadowRoot.storyName = 'Wrapped in shadow root';
diff --git a/src/collapse/collapse.test.tsx b/src/collapse/collapse.test.tsx
index 7cf96edcdad..0ced3f48344 100644
--- a/src/collapse/collapse.test.tsx
+++ b/src/collapse/collapse.test.tsx
@@ -2,11 +2,14 @@ import {type PropsWithChildren, useState} from 'react';
 import * as React from 'react';
 import {render, screen, waitFor} from '@testing-library/react';
 import userEvent from '@testing-library/user-event';
+import {afterAll, describe, expect} from 'vitest';
+import {screen as shadowScreen} from 'shadow-dom-testing-library';
 
-import {COLLAPSE_CONTENT_CONTAINER_TEST_ID} from './consts';
+import {COLLAPSE_CONTENT_CONTAINER_TEST_ID, COLLAPSE_CONTENT_TEST_ID} from './consts';
 import {Collapse} from './collapse';
 import {CollapseContent} from './collapse-content';
 import {CollapseControl} from './collapse-control';
+import {ShadowRootWrap} from './shadow-root-test-helpers';
 
 import styles from './collapse.css';
 
@@ -157,4 +160,106 @@ describe('<Collapse />', () => {
 
     expect(content).to.contain.text(textMock);
   });
+
+  type PartialObserverEntry = Partial<{
+    [K in keyof ResizeObserverEntry]: Partial<ResizeObserverEntry[K]>;
+  }>;
+
+  describe('with ResizeObserver', () => {
+    let observerCallback: (entries: PartialObserverEntry[]) => void;
+    const observeMock = vi.fn();
+    const disconnectMock = vi.fn();
+    const unobserveMock = vi.fn();
+
+    const originalObserver = global.ResizeObserver;
+
+    beforeEach(() => {
+      global.ResizeObserver = vi.fn(
+        class {
+          constructor(cb: ResizeObserverCallback) {
+            observerCallback = cb as typeof observerCallback;
+          }
+
+          observe = observeMock;
+          disconnect = disconnectMock;
+          unobserve = unobserveMock;
+        },
+      );
+    });
+
+    afterEach(() => {
+      vi.clearAllMocks();
+    });
+
+    afterAll(() => {
+      global.ResizeObserver = originalObserver;
+    });
+
+    it('should track height via ResizeObserver and cleanup on unmount', async () => {
+      const {unmount} = renderComponent();
+      const button = screen.getByRole('button', {name: 'Show text'});
+      const contentContainer = screen.getByTestId(COLLAPSE_CONTENT_CONTAINER_TEST_ID);
+      const contentInner = screen.getByTestId(COLLAPSE_CONTENT_TEST_ID);
+
+      expect(observeMock).toHaveBeenCalledWith(contentInner);
+
+      // simulate resize observer firing on element mounting
+      observerCallback([
+        {
+          target: contentInner,
+          contentRect: {height: 150},
+        },
+      ]);
+
+      expect(contentContainer.style.height).to.equal('0px');
+
+      await userEvent.click(button);
+
+      expect(contentContainer.style.height).to.equal('150px');
+
+      await userEvent.click(button);
+
+      expect(contentContainer.style.height).to.equal('0px');
+
+      unmount();
+
+      expect(disconnectMock).to.toHaveBeenCalledTimes(1);
+    });
+
+    it('expect to work from inside shadowroot', async () => {
+      const {unmount} = render(
+        <ShadowRootWrap>
+          <Dummy minHeight={0} disableAnimation={false} controlAsFunc={false} defaultCollapsed collapsed={null} />
+        </ShadowRootWrap>,
+      );
+
+      const button = shadowScreen.getByShadowRole('button', {name: 'Show text'});
+      const contentContainer = shadowScreen.getByShadowTestId(COLLAPSE_CONTENT_CONTAINER_TEST_ID);
+      const contentInner = shadowScreen.getByShadowTestId(COLLAPSE_CONTENT_TEST_ID);
+
+      expect(observeMock).toHaveBeenCalledWith(contentInner);
+
+      // simulate resize observer firing on element mounting
+      observerCallback([
+        {
+          target: contentInner,
+          contentRect: {height: 150},
+        },
+      ]);
+
+      expect(contentContainer.style.height).to.equal('0px');
+
+      await userEvent.click(button);
+
+      expect(contentContainer.style.height).to.equal('150px');
+
+      await userEvent.click(button);
+
+      expect(contentContainer.style.height).to.equal('0px');
+
+      unmount();
+
+      expect(disconnectMock).to.toHaveBeenCalledTimes(1);
+    });
+  });
 });
diff --git a/src/collapse/shadow-root-test-helpers.tsx b/src/collapse/shadow-root-test-helpers.tsx
new file mode 100644
index 00000000000..5d202987686
--- /dev/null
+++ b/src/collapse/shadow-root-test-helpers.tsx
@@ -0,0 +1,56 @@
+import {type FC, type PropsWithChildren, StrictMode} from 'react';
+import {createRoot} from 'react-dom/client';
+
+export const createShadowRootStyleSheet = (ruleTitles: string[], ruleCount?: number) => {
+  const ruleCountLocal = ruleCount ?? ruleTitles.length;
+
+  for (const styleSheet of document.styleSheets) {
+    if (styleSheet.cssRules.length === ruleCountLocal) {
+      const matchesArr = ruleTitles.map((rule, i) => Boolean(styleSheet.cssRules.item(i)?.cssText.includes(rule)));
+
+      if (!matchesArr.includes(false)) {
+        const newStyleSheet = new CSSStyleSheet();
+        for (const cssRule of styleSheet.cssRules) {
+          newStyleSheet.insertRule(cssRule.cssText);
+        }
+        return newStyleSheet;
+      }
+    }
+  }
+
+  throw new Error('Was unable to match any stylesheets for Collapse component');
+};
+
+export const ShadowRootWrap: FC<PropsWithChildren<{adoptedStyleSheets?: CSSStyleSheet[]}>> = ({
+  children,
+  adoptedStyleSheets,
+}) => {
+  const refCb = (shadowRootParent: HTMLDivElement) => {
+    let shadowRoot;
+    if (shadowRootParent.shadowRoot) {
+      shadowRoot = shadowRootParent.shadowRoot;
+    } else {
+      shadowRoot = shadowRootParent.attachShadow({
+        mode: 'open',
+      });
+      if (adoptedStyleSheets) {
+        shadowRoot.adoptedStyleSheets = adoptedStyleSheets;
+      }
+    }
+
+    const rootElem = document.createElement('div');
+    shadowRoot.replaceChildren(rootElem);
+
+    const rootComponent = createRoot(rootElem);
+
+    rootComponent.render(<StrictMode>{children}</StrictMode>);
+
+    return () => {
+      queueMicrotask(() => {
+        rootComponent.unmount();
+      });
+    };
+  };
+
+  return <div ref={refCb} />;
+};