From a537274a42d0bb152fd2ba4a3df88374ce546cff Mon Sep 17 00:00:00 2001
From: Eugene Olonov <eugeneolonov@microsoft.com>
Date: Thu, 12 Nov 2026 11:43:58 -0800
Subject: [PATCH 1/4] Test that Web Chat keeps its styles when an Activity
 hides and shows it

Also in Strict Mode on React 18 and 19, and when one of two Web Chats sharing styles unmounts.
---
 .../html2/basic/twoWebChats.unmountOne.html   |  83 ++++++++++++++++++
 .../twoWebChats.unmountOne.html.snap-1.png    | Bin 0 -> 12149 bytes
 .../twoWebChats.unmountOne.html.snap-2.png    | Bin 0 -> 8850 bytes
 .../react19/activity.hideShow.fluent.html     |  74 ++++++++++++++++
 .../activity.hideShow.fluent.html.snap-1.png  | Bin 0 -> 5576 bytes
 .../activity.hideShow.fluent.html.snap-2.png  | Bin 0 -> 5576 bytes
 .../html2/react19/activity.hideShow.html      |  75 ++++++++++++++++
 .../react19/activity.hideShow.html.snap-1.png | Bin 0 -> 4932 bytes
 .../react19/activity.hideShow.html.snap-2.png | Bin 0 -> 4932 bytes
 .../activity.hideShow.styleOptions.html       |  77 ++++++++++++++++
 ...vity.hideShow.styleOptions.html.snap-1.png | Bin 0 -> 4932 bytes
 .../react19/strictMode.unmount.styles.html    |  64 ++++++++++++++
 .../strictMode.unmount.styles.html.snap-1.png | Bin 0 -> 4932 bytes
 .../html2/strictMode/unmount.styles.html      |  64 ++++++++++++++
 .../strictMode/unmount.styles.html.snap-1.png | Bin 0 -> 4932 bytes
 15 files changed, 437 insertions(+)
 create mode 100644 __tests__/html2/basic/twoWebChats.unmountOne.html
 create mode 100644 __tests__/html2/basic/twoWebChats.unmountOne.html.snap-1.png
 create mode 100644 __tests__/html2/basic/twoWebChats.unmountOne.html.snap-2.png
 create mode 100644 __tests__/html2/react19/activity.hideShow.fluent.html
 create mode 100644 __tests__/html2/react19/activity.hideShow.fluent.html.snap-1.png
 create mode 100644 __tests__/html2/react19/activity.hideShow.fluent.html.snap-2.png
 create mode 100644 __tests__/html2/react19/activity.hideShow.html
 create mode 100644 __tests__/html2/react19/activity.hideShow.html.snap-1.png
 create mode 100644 __tests__/html2/react19/activity.hideShow.html.snap-2.png
 create mode 100644 __tests__/html2/react19/activity.hideShow.styleOptions.html
 create mode 100644 __tests__/html2/react19/activity.hideShow.styleOptions.html.snap-1.png
 create mode 100644 __tests__/html2/react19/strictMode.unmount.styles.html
 create mode 100644 __tests__/html2/react19/strictMode.unmount.styles.html.snap-1.png
 create mode 100644 __tests__/html2/strictMode/unmount.styles.html
 create mode 100644 __tests__/html2/strictMode/unmount.styles.html.snap-1.png

diff --git a/__tests__/html2/basic/twoWebChats.unmountOne.html b/__tests__/html2/basic/twoWebChats.unmountOne.html
new file mode 100644
index 0000000000..1ebee8f68f
--- /dev/null
+++ b/__tests__/html2/basic/twoWebChats.unmountOne.html
@@ -0,0 +1,83 @@
+<!doctype html>
+<html lang="en-US">
+  <head>
+    <title>Two Web Chats share their styles: the one left keeps them when the other is unmounted</title>
+    <link href="/assets/index.css" rel="stylesheet" type="text/css" />
+    <style>
+      #webchat > div {
+        height: 50%;
+      }
+    </style>
+  </head>
+  <body>
+    <main id="webchat">
+      <div id="webchat-1"></div>
+      <div id="webchat-2"></div>
+    </main>
+    <script type="importmap">
+      {
+        "imports": {
+          "@testduet/wait-for": "https://esm.sh/@testduet/wait-for",
+          "botframework-webchat": "/__dist__/packages/bundle/static/botframework-webchat.js",
+          "react": "/__dist__/packages/bundle/static/react.js",
+          "react-dom": "/__dist__/packages/bundle/static/react-dom.js",
+          "react-dom/client": "/__dist__/packages/bundle/static/react-dom/client.js"
+        }
+      }
+    </script>
+    <script type="module">
+      import '/test-harness.mjs';
+      import '/test-page-object.mjs';
+
+      import { waitFor } from '@testduet/wait-for';
+      import { createStoreWithOptions, ReactWebChat, testIds } from 'botframework-webchat';
+      import { createElement } from 'react';
+      import { createRoot } from 'react-dom/client';
+
+      run(async function () {
+        // TODO: This is for `createDirectLineEmulator` and `pageElements` only, should find ways to eliminate this line.
+        window.WebChat = { createStoreWithOptions, testIds };
+
+        // `pageConditions.numActivitiesShown()` only counts the first transcript.
+        const getNumActivities = () => document.querySelectorAll('.webchat__basic-transcript__activity').length;
+        // Only Web Chat's styles hide the file input of the upload button.
+        const getFileInputOpacities = () =>
+          Array.from(
+            document.querySelectorAll('.webchat__upload-button--file-input'),
+            element => getComputedStyle(element).opacity
+          );
+
+        // GIVEN: Two Web Chats with the same nonce and styles root (both default), so they share their styles.
+        // The first one hides its send box: two unnamed send box landmarks would not be unique.
+        const root1 = createRoot(document.getElementById('webchat-1'));
+        const webChat1 = testHelpers.createDirectLineEmulator();
+        const webChat2 = testHelpers.createDirectLineEmulator();
+
+        root1.render(createElement(ReactWebChat, { ...webChat1, styleOptions: { hideSendBox: true } }));
+        createRoot(document.getElementById('webchat-2')).render(createElement(ReactWebChat, webChat2));
+
+        await pageConditions.uiConnected();
+
+        await webChat1.directLine.emulateIncomingActivity('Hello from the first Web Chat.');
+        await webChat2.directLine.emulateIncomingActivity('Hello from the second Web Chat.');
+        await waitFor(() => expect(getNumActivities()).toBe(2));
+
+        expect(getFileInputOpacities()).toEqual(['0']);
+
+        // THEN: Both Web Chats show their messages with their styles, the second one with its send box.
+        await host.snapshot('local');
+
+        // WHEN: The first Web Chat is unmounted.
+        root1.unmount();
+
+        expect(getNumActivities()).toBe(1);
+
+        // THEN: The second Web Chat keeps the styles.
+        expect(getFileInputOpacities()).toEqual(['0']);
+
+        // THEN: Only the second Web Chat is shown, with its styles.
+        await host.snapshot('local');
+      });
+    </script>
+  </body>
+</html>
diff --git a/__tests__/html2/basic/twoWebChats.unmountOne.html.snap-1.png b/__tests__/html2/basic/twoWebChats.unmountOne.html.snap-1.png
new file mode 100644
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diff --git a/__tests__/html2/react19/activity.hideShow.fluent.html b/__tests__/html2/react19/activity.hideShow.fluent.html
new file mode 100644
index 0000000000..608e62f9ce
--- /dev/null
+++ b/__tests__/html2/react19/activity.hideShow.fluent.html
@@ -0,0 +1,74 @@
+<!doctype html>
+<html lang="en-US">
+  <head>
+    <title>React 19: Web Chat with the Fluent theme keeps its styles when an &lt;Activity&gt; hides and shows it</title>
+    <link href="/assets/index.css" rel="stylesheet" type="text/css" />
+    <script type="importmap">
+      {
+        "imports": {
+          "@testduet/wait-for": "https://esm.sh/@testduet/wait-for",
+          "react": "https://esm.sh/react@19.3.1?dev",
+          "react-dom": "https://esm.sh/react-dom@19.3.1?dev",
+          "react-dom/client": "https://esm.sh/react-dom@19.3.1/client?dev"
+        }
+      }
+    </script>
+    <script crossorigin="anonymous" src="/test-harness.js"></script>
+    <script crossorigin="anonymous" src="/test-page-object.js"></script>
+    <script type="module">
+      // React 19 has no UMD build: the IIFE builds of Web Chat and the Fluent theme use `window.React` and `window.ReactDOM`.
+      import React from 'react';
+      import ReactDOM from 'react-dom';
+
+      window.React = React;
+      window.ReactDOM = ReactDOM;
+    </script>
+    <script crossorigin="anonymous" defer src="/__dist__/webchat-es5.js"></script>
+    <script crossorigin="anonymous" defer src="/__dist__/botframework-webchat-fluent-theme.development.js"></script>
+  </head>
+  <body>
+    <main id="webchat"></main>
+    <script type="module">
+      import { waitFor } from '@testduet/wait-for';
+      import { Activity, createElement, version } from 'react';
+      import { createRoot } from 'react-dom/client';
+
+      run(async function () {
+        const {
+          WebChat: { FluentThemeProvider, ReactWebChat }
+        } = window; // Imports in UMD fashion.
+
+        const { directLine, store } = testHelpers.createDirectLineEmulator();
+
+        // GIVEN: React 19.2 or later: a hidden <Activity> runs the cleanup of the effects of its children, and keeps them.
+        expect(version).toBe('19.3.1');
+
+        const root = createRoot(document.getElementById('webchat'));
+        // The same element each time: showing Web Chat again does not re-render it, only its effects run again.
+        const webChat = createElement(FluentThemeProvider, {}, createElement(ReactWebChat, { directLine, store }));
+        const render = mode => root.render(createElement(Activity, { mode }, webChat));
+
+        // WHEN: Web Chat with the Fluent theme is rendered in a visible <Activity>.
+        render('visible');
+
+        await pageConditions.uiConnected();
+
+        // THEN: Web Chat shows the send box of the Fluent theme at the bottom.
+        await host.snapshot('local');
+
+        // WHEN: The <Activity> hides Web Chat.
+        render('hidden');
+
+        await waitFor(() => expect(pageElements.sendBoxTextBox()).toHaveProperty('offsetParent', null));
+
+        // WHEN: The <Activity> shows Web Chat again.
+        render('visible');
+
+        await waitFor(() => expect(pageElements.sendBoxTextBox()).not.toHaveProperty('offsetParent', null));
+
+        // THEN: Web Chat looks the same as before it was hidden: the send box stays at the bottom.
+        await host.snapshot('local');
+      });
+    </script>
+  </body>
+</html>
diff --git a/__tests__/html2/react19/activity.hideShow.fluent.html.snap-1.png b/__tests__/html2/react19/activity.hideShow.fluent.html.snap-1.png
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diff --git a/__tests__/html2/react19/activity.hideShow.html b/__tests__/html2/react19/activity.hideShow.html
new file mode 100644
index 0000000000..a28332e6d6
--- /dev/null
+++ b/__tests__/html2/react19/activity.hideShow.html
@@ -0,0 +1,75 @@
+<!doctype html>
+<html lang="en-US">
+  <head>
+    <title>React 19: Web Chat keeps its styles when an &lt;Activity&gt; hides and shows it</title>
+    <link href="/assets/index.css" rel="stylesheet" type="text/css" />
+  </head>
+  <body>
+    <main id="webchat"></main>
+    <script type="importmap">
+      {
+        "imports": {
+          "@testduet/wait-for": "https://esm.sh/@testduet/wait-for",
+          "botframework-webchat": "/__dist__/packages/bundle/static/botframework-webchat.js",
+          "react": "https://esm.sh/react@19.3.1?dev",
+          "react-dom": "https://esm.sh/react-dom@19.3.1?dev",
+          "react-dom/client": "https://esm.sh/react-dom@19.3.1/client?dev"
+        }
+      }
+    </script>
+    <script type="module">
+      import '/test-harness.mjs';
+      import '/test-page-object.mjs';
+
+      import { waitFor } from '@testduet/wait-for';
+      import { createStoreWithOptions, ReactWebChat, testIds } from 'botframework-webchat';
+      import { Activity, createElement, version } from 'react';
+      import { createRoot } from 'react-dom/client';
+
+      run(async function () {
+        // TODO: This is for `createDirectLineEmulator` and `pageElements` only, should find ways to eliminate this line.
+        window.WebChat = { createStoreWithOptions, testIds };
+
+        const { directLine, store } = testHelpers.createDirectLineEmulator();
+
+        // GIVEN: React 19.2 or later: a hidden <Activity> runs the cleanup of the effects of its children, and keeps them.
+        expect(version).toBe('19.3.1');
+
+        const root = createRoot(document.getElementById('webchat'));
+        // The same element each time: showing Web Chat again does not re-render it, only its effects run again.
+        const webChat = createElement(ReactWebChat, { directLine, store });
+        const render = mode => root.render(createElement(Activity, { mode }, webChat));
+
+        // Only Web Chat's styles hide the file input of the upload button.
+        const getFileInputOpacity = () =>
+          getComputedStyle(document.querySelector('.webchat__upload-button--file-input')).opacity;
+
+        // WHEN: Web Chat is rendered in a visible <Activity>.
+        render('visible');
+
+        await pageConditions.uiConnected();
+
+        expect(getFileInputOpacity()).toBe('0');
+
+        // THEN: Web Chat shows the send box with its styles.
+        await host.snapshot('local');
+
+        // WHEN: The <Activity> hides Web Chat.
+        render('hidden');
+
+        await waitFor(() => expect(pageElements.sendBoxTextBox()).toHaveProperty('offsetParent', null));
+
+        // WHEN: The <Activity> shows Web Chat again.
+        render('visible');
+
+        await waitFor(() => expect(pageElements.sendBoxTextBox()).not.toHaveProperty('offsetParent', null));
+
+        // THEN: Web Chat keeps its styles: the file input is still hidden.
+        await waitFor(() => expect(getFileInputOpacity()).toBe('0'));
+
+        // THEN: Web Chat looks the same as before it was hidden.
+        await host.snapshot('local');
+      });
+    </script>
+  </body>
+</html>
diff --git a/__tests__/html2/react19/activity.hideShow.html.snap-1.png b/__tests__/html2/react19/activity.hideShow.html.snap-1.png
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diff --git a/__tests__/html2/react19/activity.hideShow.styleOptions.html b/__tests__/html2/react19/activity.hideShow.styleOptions.html
new file mode 100644
index 0000000000..2cf2cc1370
--- /dev/null
+++ b/__tests__/html2/react19/activity.hideShow.styleOptions.html
@@ -0,0 +1,77 @@
+<!doctype html>
+<html lang="en-US">
+  <head>
+    <title>React 19: Web Chat applies the style options changed while an &lt;Activity&gt; hides it</title>
+    <link href="/assets/index.css" rel="stylesheet" type="text/css" />
+  </head>
+  <body>
+    <main id="webchat"></main>
+    <script type="importmap">
+      {
+        "imports": {
+          "@testduet/wait-for": "https://esm.sh/@testduet/wait-for",
+          "botframework-webchat": "/__dist__/packages/bundle/static/botframework-webchat.js",
+          "react": "https://esm.sh/react@19.3.1?dev",
+          "react-dom": "https://esm.sh/react-dom@19.3.1?dev",
+          "react-dom/client": "https://esm.sh/react-dom@19.3.1/client?dev"
+        }
+      }
+    </script>
+    <script type="module">
+      import '/test-harness.mjs';
+      import '/test-page-object.mjs';
+
+      import { waitFor } from '@testduet/wait-for';
+      import { createStoreWithOptions, ReactWebChat, testIds } from 'botframework-webchat';
+      import { Activity, createElement, version } from 'react';
+      import { createRoot } from 'react-dom/client';
+
+      run(async function () {
+        // TODO: This is for `createDirectLineEmulator` and `pageElements` only, should find ways to eliminate this line.
+        window.WebChat = { createStoreWithOptions, testIds };
+
+        const { directLine, store } = testHelpers.createDirectLineEmulator();
+
+        // GIVEN: React 19.2 or later: a hidden <Activity> runs the cleanup of the effects of its children, and keeps them.
+        expect(version).toBe('19.3.1');
+
+        const root = createRoot(document.getElementById('webchat'));
+        const render = (mode, styleOptions) =>
+          root.render(
+            createElement(Activity, { mode }, createElement(ReactWebChat, { directLine, store, styleOptions }))
+          );
+
+        // WHEN: Web Chat is rendered in a visible <Activity>.
+        render('visible', {});
+
+        await pageConditions.uiConnected();
+
+        // WHEN: The <Activity> hides Web Chat.
+        render('hidden', {});
+
+        await waitFor(() => expect(pageElements.sendBoxTextBox()).toHaveProperty('offsetParent', null));
+
+        const getSurface = () => document.querySelector('.webchat__surface');
+        const surfaceClassName = getSurface().className;
+
+        // WHEN: The host changes the background color while Web Chat is hidden.
+        render('hidden', { backgroundColor: '#FFFFE0' }); // Light yellow.
+
+        // React renders hidden children at a lower priority: the new background color is a new class name.
+        await waitFor(() => expect(getSurface().className).not.toBe(surfaceClassName));
+
+        // WHEN: The <Activity> shows Web Chat again.
+        render('visible', { backgroundColor: '#FFFFE0' });
+
+        await waitFor(() => expect(pageElements.sendBoxTextBox()).not.toHaveProperty('offsetParent', null));
+
+        // THEN: Web Chat applies the background color, and keeps the styles it had before: the file input is still hidden.
+        await waitFor(() => expect(getComputedStyle(getSurface()).backgroundColor).toBe('rgb(255, 255, 224)'));
+        expect(getComputedStyle(document.querySelector('.webchat__upload-button--file-input')).opacity).toBe('0');
+
+        // THEN: Web Chat shows the send box on a light yellow background.
+        await host.snapshot('local');
+      });
+    </script>
+  </body>
+</html>
diff --git a/__tests__/html2/react19/activity.hideShow.styleOptions.html.snap-1.png b/__tests__/html2/react19/activity.hideShow.styleOptions.html.snap-1.png
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diff --git a/__tests__/html2/react19/strictMode.unmount.styles.html b/__tests__/html2/react19/strictMode.unmount.styles.html
new file mode 100644
index 0000000000..4fae2167b9
--- /dev/null
+++ b/__tests__/html2/react19/strictMode.unmount.styles.html
@@ -0,0 +1,64 @@
+<!doctype html>
+<html lang="en-US">
+  <head>
+    <title>React 19 in Strict Mode: Web Chat keeps its styles, and removes them when unmounted</title>
+    <link href="/assets/index.css" rel="stylesheet" type="text/css" />
+  </head>
+  <body>
+    <main id="webchat"></main>
+    <script type="importmap">
+      {
+        "imports": {
+          "@testduet/wait-for": "https://esm.sh/@testduet/wait-for",
+          "botframework-webchat": "/__dist__/packages/bundle/static/botframework-webchat.js",
+          "react": "https://esm.sh/react@19.3.1?dev",
+          "react-dom": "https://esm.sh/react-dom@19.3.1?dev",
+          "react-dom/client": "https://esm.sh/react-dom@19.3.1/client?dev"
+        }
+      }
+    </script>
+    <script type="module">
+      import '/test-harness.mjs';
+      import '/test-page-object.mjs';
+
+      import { waitFor } from '@testduet/wait-for';
+      import { createStoreWithOptions, ReactWebChat, testIds } from 'botframework-webchat';
+      import { createElement, StrictMode, version } from 'react';
+      import { createRoot } from 'react-dom/client';
+
+      run(async function () {
+        // TODO: This is for `createDirectLineEmulator` and `pageElements` only, should find ways to eliminate this line.
+        window.WebChat = { createStoreWithOptions, testIds };
+
+        const { directLine, store } = testHelpers.createDirectLineEmulator();
+
+        // Web Chat adds its styles as <style> elements to `styleOptions.stylesRoot`, which defaults to <head>.
+        const getNumStyleElements = () => document.head.querySelectorAll('style').length;
+
+        // GIVEN: The development build of React 19, which mounts, unmounts and mounts again in Strict Mode (React 18: strictMode/unmount.styles.html).
+        expect(version).toBe('19.3.1');
+
+        const numStyleElementsBeforeRender = getNumStyleElements();
+        const root = createRoot(document.getElementById('webchat'));
+
+        // WHEN: Web Chat is rendered in Strict Mode.
+        root.render(createElement(StrictMode, {}, createElement(ReactWebChat, { directLine, store })));
+
+        await pageConditions.uiConnected();
+
+        // THEN: Web Chat has its styles: only they hide the file input of the upload button.
+        expect(getNumStyleElements()).toBeGreaterThan(numStyleElementsBeforeRender);
+        expect(getComputedStyle(document.querySelector('.webchat__upload-button--file-input')).opacity).toBe('0');
+
+        // THEN: Web Chat shows the send box with its styles.
+        await host.snapshot('local');
+
+        // WHEN: Web Chat is unmounted.
+        root.unmount();
+
+        // THEN: Web Chat removes all the <style> elements it added.
+        expect(getNumStyleElements()).toBe(numStyleElementsBeforeRender);
+      });
+    </script>
+  </body>
+</html>
diff --git a/__tests__/html2/react19/strictMode.unmount.styles.html.snap-1.png b/__tests__/html2/react19/strictMode.unmount.styles.html.snap-1.png
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diff --git a/__tests__/html2/strictMode/unmount.styles.html b/__tests__/html2/strictMode/unmount.styles.html
new file mode 100644
index 0000000000..b2b97545f0
--- /dev/null
+++ b/__tests__/html2/strictMode/unmount.styles.html
@@ -0,0 +1,64 @@
+<!doctype html>
+<html lang="en-US">
+  <head>
+    <title>Strict Mode: Web Chat keeps its styles on React 18, and removes them when unmounted</title>
+    <link href="/assets/index.css" rel="stylesheet" type="text/css" />
+  </head>
+  <body>
+    <main id="webchat"></main>
+    <script type="importmap">
+      {
+        "imports": {
+          "@testduet/wait-for": "https://esm.sh/@testduet/wait-for",
+          "botframework-webchat": "/__dist__/packages/bundle/static/botframework-webchat.js",
+          "react": "/__dist__/packages/bundle/static/react.js",
+          "react-dom": "/__dist__/packages/bundle/static/react-dom.js",
+          "react-dom/client": "/__dist__/packages/bundle/static/react-dom/client.js"
+        }
+      }
+    </script>
+    <script type="module">
+      import '/test-harness.mjs';
+      import '/test-page-object.mjs';
+
+      import { waitFor } from '@testduet/wait-for';
+      import { createStoreWithOptions, ReactWebChat, testIds } from 'botframework-webchat';
+      import { createElement, StrictMode, version } from 'react';
+      import { createRoot } from 'react-dom/client';
+
+      run(async function () {
+        // TODO: This is for `createDirectLineEmulator` and `pageElements` only, should find ways to eliminate this line.
+        window.WebChat = { createStoreWithOptions, testIds };
+
+        const { directLine, store } = testHelpers.createDirectLineEmulator();
+
+        // Web Chat adds its styles as <style> elements to `styleOptions.stylesRoot`, which defaults to <head>.
+        const getNumStyleElements = () => document.head.querySelectorAll('style').length;
+
+        // GIVEN: The development build of React 18, which mounts, unmounts and mounts again in Strict Mode (React 19: react19/strictMode.unmount.styles.html).
+        expect(version).toBe('18.3.1');
+
+        const numStyleElementsBeforeRender = getNumStyleElements();
+        const root = createRoot(document.getElementById('webchat'));
+
+        // WHEN: Web Chat is rendered in Strict Mode.
+        root.render(createElement(StrictMode, {}, createElement(ReactWebChat, { directLine, store })));
+
+        await pageConditions.uiConnected();
+
+        // THEN: Web Chat has its styles: only they hide the file input of the upload button.
+        expect(getNumStyleElements()).toBeGreaterThan(numStyleElementsBeforeRender);
+        expect(getComputedStyle(document.querySelector('.webchat__upload-button--file-input')).opacity).toBe('0');
+
+        // THEN: Web Chat shows the send box with its styles.
+        await host.snapshot('local');
+
+        // WHEN: Web Chat is unmounted.
+        root.unmount();
+
+        // THEN: Web Chat removes all the <style> elements it added.
+        expect(getNumStyleElements()).toBe(numStyleElementsBeforeRender);
+      });
+    </script>
+  </body>
+</html>
diff --git a/__tests__/html2/strictMode/unmount.styles.html.snap-1.png b/__tests__/html2/strictMode/unmount.styles.html.snap-1.png
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From 5108d2c951198e55f8907a632281058ad8d1c1d9 Mon Sep 17 00:00:00 2001
From: Eugene Olonov <eugeneolonov@microsoft.com>
Date: Thu, 12 Nov 2026 11:43:59 -0800
Subject: [PATCH 2/4] Keep Web Chat styles when an Activity hides and shows it

useEmotion() counted references in useMemo(), during render. A hidden <Activity> runs the effect cleanup, which
removed the style elements, and showing it runs the effect again without rendering, so nothing put them back.
Count in a layout effect instead, and rebuild the rules from the registered styles when acquired after the last
release.
---
 .../src/hooks/internal/useEmotion.ts          | 39 ++++++++++++-------
 1 file changed, 25 insertions(+), 14 deletions(-)

diff --git a/packages/component/src/hooks/internal/useEmotion.ts b/packages/component/src/hooks/internal/useEmotion.ts
index 67ad06e6bd..5b57ed5ef2 100644
--- a/packages/component/src/hooks/internal/useEmotion.ts
+++ b/packages/component/src/hooks/internal/useEmotion.ts
@@ -1,23 +1,35 @@
 import createEmotion from '@emotion/css/create-instance';
-import { useEffect, useMemo } from 'react';
+import { useLayoutEffect, useMemo } from 'react';
 import createCSSKey from '../../Utils/createCSSKey';
 
 const sharedEmotionInstances = [];
 
 export default function useEmotion(nonce?: string, container?: Node) {
-  const emotion = useMemo(() => {
-    const sharedEmotion = sharedEmotionInstances.find(
-      ({ sheet }) => sheet.nonce === nonce && sheet.container === container
-    );
-    const emotion = sharedEmotion ?? createEmotion({ container, key: `webchat--css-${createCSSKey()}`, nonce });
+  const emotion = useMemo(
+    () =>
+      sharedEmotionInstances.find(({ sheet }) => sheet.nonce === nonce && sheet.container === container) ??
+      createEmotion({ container, key: `webchat--css-${createCSSKey()}`, nonce }),
+    [container, nonce]
+  );
 
-    sharedEmotionInstances.push(emotion);
+  // Ref count in the effect, not in render: a hidden <Activity> (React 19.2+) and Strict Mode run the cleanup, then the
+  // effect again, without rendering again.
+  // Layout effect: restores the styles before paint, and before <InjectStyleElements> appends its own, as on mount.
+  useLayoutEffect(() => {
+    const { cache, sheet } = emotion;
 
-    return emotion;
-  }, [container, nonce]);
+    // The last release removed the style elements, but the class names are still in use: insert their rules again.
+    if (!sharedEmotionInstances.includes(emotion) && sheet.tags.some(tag => !tag.isConnected)) {
+      sheet.flush();
+
+      for (const [className, styles] of Object.entries(cache.registered)) {
+        cache.insert(`.${className}`, { name: className, styles }, sheet, false);
+      }
+    }
 
-  useEffect(
-    () => () => {
+    sharedEmotionInstances.push(emotion);
+
+    return () => {
       const index = sharedEmotionInstances.lastIndexOf(emotion);
 
       // Reduce ref count for the specific emotion instance.
@@ -29,9 +41,8 @@ export default function useEmotion(nonce?: string, container?: Node) {
           child.remove();
         }
       }
-    },
-    [emotion]
-  );
+    };
+  }, [emotion]);
 
   return emotion;
 }

From b89329899437e7617f6ac28da98e4a197f08b9ce Mon Sep 17 00:00:00 2001
From: Eugene Olonov <eugeneolonov@microsoft.com>
Date: Thu, 12 Nov 2026 12:11:07 -0800
Subject: [PATCH 3/4] Test styles with snapshots and style counts, and a shared
 sheet after an Activity showed Web Chat again

Drop the computed-style assertions. The new page fails when the reference count goes back into render.
---
 .../html2/basic/twoWebChats.unmountOne.html   |  15 ++-
 .../html2/react19/activity.hideShow.html      |  11 +--
 .../activity.hideShow.sharedStyles.html       |  91 ++++++++++++++++++
 ...vity.hideShow.sharedStyles.html.snap-1.png | Bin 0 -> 8859 bytes
 ...vity.hideShow.sharedStyles.html.snap-2.png | Bin 0 -> 4932 bytes
 .../activity.hideShow.styleOptions.html       |   6 +-
 .../react19/strictMode.unmount.styles.html    |   3 +-
 .../html2/strictMode/unmount.styles.html      |   3 +-
 8 files changed, 105 insertions(+), 24 deletions(-)
 create mode 100644 __tests__/html2/react19/activity.hideShow.sharedStyles.html
 create mode 100644 __tests__/html2/react19/activity.hideShow.sharedStyles.html.snap-1.png
 create mode 100644 __tests__/html2/react19/activity.hideShow.sharedStyles.html.snap-2.png

diff --git a/__tests__/html2/basic/twoWebChats.unmountOne.html b/__tests__/html2/basic/twoWebChats.unmountOne.html
index 1ebee8f68f..3b1f12afd0 100644
--- a/__tests__/html2/basic/twoWebChats.unmountOne.html
+++ b/__tests__/html2/basic/twoWebChats.unmountOne.html
@@ -40,12 +40,9 @@
 
         // `pageConditions.numActivitiesShown()` only counts the first transcript.
         const getNumActivities = () => document.querySelectorAll('.webchat__basic-transcript__activity').length;
-        // Only Web Chat's styles hide the file input of the upload button.
-        const getFileInputOpacities = () =>
-          Array.from(
-            document.querySelectorAll('.webchat__upload-button--file-input'),
-            element => getComputedStyle(element).opacity
-          );
+        // The <style> elements of the styles the two Web Chats share.
+        const getNumSharedStyleElements = () =>
+          document.head.querySelectorAll('style[data-emotion^="webchat--css-"]').length;
 
         // GIVEN: Two Web Chats with the same nonce and styles root (both default), so they share their styles.
         // The first one hides its send box: two unnamed send box landmarks would not be unique.
@@ -62,7 +59,7 @@
         await webChat2.directLine.emulateIncomingActivity('Hello from the second Web Chat.');
         await waitFor(() => expect(getNumActivities()).toBe(2));
 
-        expect(getFileInputOpacities()).toEqual(['0']);
+        expect(getNumSharedStyleElements()).toBe(1);
 
         // THEN: Both Web Chats show their messages with their styles, the second one with its send box.
         await host.snapshot('local');
@@ -72,8 +69,8 @@
 
         expect(getNumActivities()).toBe(1);
 
-        // THEN: The second Web Chat keeps the styles.
-        expect(getFileInputOpacities()).toEqual(['0']);
+        // THEN: The second Web Chat keeps the shared <style> element.
+        expect(getNumSharedStyleElements()).toBe(1);
 
         // THEN: Only the second Web Chat is shown, with its styles.
         await host.snapshot('local');
diff --git a/__tests__/html2/react19/activity.hideShow.html b/__tests__/html2/react19/activity.hideShow.html
index a28332e6d6..a70b087ecf 100644
--- a/__tests__/html2/react19/activity.hideShow.html
+++ b/__tests__/html2/react19/activity.hideShow.html
@@ -40,16 +40,15 @@
         const webChat = createElement(ReactWebChat, { directLine, store });
         const render = mode => root.render(createElement(Activity, { mode }, webChat));
 
-        // Only Web Chat's styles hide the file input of the upload button.
-        const getFileInputOpacity = () =>
-          getComputedStyle(document.querySelector('.webchat__upload-button--file-input')).opacity;
+        // The <style> element of Web Chat's emotion styles, added to `styleOptions.stylesRoot`, which defaults to <head>.
+        const getNumStyleElements = () => document.head.querySelectorAll('style[data-emotion^="webchat--css-"]').length;
 
         // WHEN: Web Chat is rendered in a visible <Activity>.
         render('visible');
 
         await pageConditions.uiConnected();
 
-        expect(getFileInputOpacity()).toBe('0');
+        const numStyleElements = getNumStyleElements();
 
         // THEN: Web Chat shows the send box with its styles.
         await host.snapshot('local');
@@ -64,8 +63,8 @@
 
         await waitFor(() => expect(pageElements.sendBoxTextBox()).not.toHaveProperty('offsetParent', null));
 
-        // THEN: Web Chat keeps its styles: the file input is still hidden.
-        await waitFor(() => expect(getFileInputOpacity()).toBe('0'));
+        // THEN: Web Chat has its <style> element back.
+        expect(getNumStyleElements()).toBe(numStyleElements);
 
         // THEN: Web Chat looks the same as before it was hidden.
         await host.snapshot('local');
diff --git a/__tests__/html2/react19/activity.hideShow.sharedStyles.html b/__tests__/html2/react19/activity.hideShow.sharedStyles.html
new file mode 100644
index 0000000000..30fc1b53e0
--- /dev/null
+++ b/__tests__/html2/react19/activity.hideShow.sharedStyles.html
@@ -0,0 +1,91 @@
+<!doctype html>
+<html lang="en-US">
+  <head>
+    <title>React 19: Web Chat shown again by an &lt;Activity&gt; keeps its shared styles when the other unmounts</title>
+    <link href="/assets/index.css" rel="stylesheet" type="text/css" />
+    <style>
+      #webchat > div {
+        height: 50%;
+      }
+    </style>
+  </head>
+  <body>
+    <main id="webchat">
+      <div id="webchat-1"></div>
+      <div id="webchat-2"></div>
+    </main>
+    <script type="importmap">
+      {
+        "imports": {
+          "@testduet/wait-for": "https://esm.sh/@testduet/wait-for",
+          "botframework-webchat": "/__dist__/packages/bundle/static/botframework-webchat.js",
+          "react": "https://esm.sh/react@19.3.1?dev",
+          "react-dom": "https://esm.sh/react-dom@19.3.1?dev",
+          "react-dom/client": "https://esm.sh/react-dom@19.3.1/client?dev"
+        }
+      }
+    </script>
+    <script type="module">
+      import '/test-harness.mjs';
+      import '/test-page-object.mjs';
+
+      import { waitFor } from '@testduet/wait-for';
+      import { createStoreWithOptions, ReactWebChat, testIds } from 'botframework-webchat';
+      import { Activity, createElement, version } from 'react';
+      import { createRoot } from 'react-dom/client';
+
+      run(async function () {
+        // TODO: This is for `createDirectLineEmulator` and `pageElements` only, should find ways to eliminate this line.
+        window.WebChat = { createStoreWithOptions, testIds };
+
+        // The <style> elements of the styles the two Web Chats share.
+        const getNumSharedStyleElements = () =>
+          document.head.querySelectorAll('style[data-emotion^="webchat--css-"]').length;
+
+        // GIVEN: React 19.2 or later: a hidden <Activity> runs the cleanup of the effects of its children, and keeps them.
+        expect(version).toBe('19.3.1');
+
+        // GIVEN: Two Web Chats with the same nonce and styles root (both default), so they share their styles.
+        // The second one hides its send box: two unnamed send box landmarks would not be unique.
+        const root1 = createRoot(document.getElementById('webchat-1'));
+        const root2 = createRoot(document.getElementById('webchat-2'));
+        const webChat1 = createElement(ReactWebChat, testHelpers.createDirectLineEmulator());
+        const webChat2 = testHelpers.createDirectLineEmulator();
+        const render1 = mode => root1.render(createElement(Activity, { mode }, webChat1));
+
+        render1('visible');
+        root2.render(createElement(ReactWebChat, { ...webChat2, styleOptions: { hideSendBox: true } }));
+
+        await pageConditions.uiConnected();
+
+        await webChat2.directLine.emulateIncomingActivity('Hello from the second Web Chat.');
+        await waitFor(() => expect(document.querySelectorAll('.webchat__basic-transcript__activity')).toHaveLength(1));
+
+        expect(getNumSharedStyleElements()).toBe(1);
+
+        // WHEN: An <Activity> hides the first Web Chat, then shows it again.
+        render1('hidden');
+
+        await waitFor(() => expect(pageElements.sendBoxTextBox()).toHaveProperty('offsetParent', null));
+
+        render1('visible');
+
+        await waitFor(() => expect(pageElements.sendBoxTextBox()).not.toHaveProperty('offsetParent', null));
+
+        // THEN: The first Web Chat shows its send box, the second one its message, both with their styles.
+        await host.snapshot('local');
+
+        // WHEN: The second Web Chat is unmounted.
+        root2.unmount();
+
+        await waitFor(() => expect(document.querySelectorAll('.webchat__basic-transcript__activity')).toHaveLength(0));
+
+        // THEN: The first Web Chat keeps the shared <style> element.
+        expect(getNumSharedStyleElements()).toBe(1);
+
+        // THEN: Only the first Web Chat is shown, with its styles.
+        await host.snapshot('local');
+      });
+    </script>
+  </body>
+</html>
diff --git a/__tests__/html2/react19/activity.hideShow.sharedStyles.html.snap-1.png b/__tests__/html2/react19/activity.hideShow.sharedStyles.html.snap-1.png
new file mode 100644
index 0000000000000000000000000000000000000000..6e43ee5068cb85c47bd32455c2aef2208602d327
GIT binary patch
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HcmV?d00001

diff --git a/__tests__/html2/react19/activity.hideShow.styleOptions.html b/__tests__/html2/react19/activity.hideShow.styleOptions.html
index 2cf2cc1370..35281e5501 100644
--- a/__tests__/html2/react19/activity.hideShow.styleOptions.html
+++ b/__tests__/html2/react19/activity.hideShow.styleOptions.html
@@ -65,11 +65,7 @@
 
         await waitFor(() => expect(pageElements.sendBoxTextBox()).not.toHaveProperty('offsetParent', null));
 
-        // THEN: Web Chat applies the background color, and keeps the styles it had before: the file input is still hidden.
-        await waitFor(() => expect(getComputedStyle(getSurface()).backgroundColor).toBe('rgb(255, 255, 224)'));
-        expect(getComputedStyle(document.querySelector('.webchat__upload-button--file-input')).opacity).toBe('0');
-
-        // THEN: Web Chat shows the send box on a light yellow background.
+        // THEN: Web Chat shows the send box with its styles, on a light yellow background.
         await host.snapshot('local');
       });
     </script>
diff --git a/__tests__/html2/react19/strictMode.unmount.styles.html b/__tests__/html2/react19/strictMode.unmount.styles.html
index 4fae2167b9..4aaaf7da04 100644
--- a/__tests__/html2/react19/strictMode.unmount.styles.html
+++ b/__tests__/html2/react19/strictMode.unmount.styles.html
@@ -46,9 +46,8 @@
 
         await pageConditions.uiConnected();
 
-        // THEN: Web Chat has its styles: only they hide the file input of the upload button.
+        // THEN: Web Chat added its <style> elements.
         expect(getNumStyleElements()).toBeGreaterThan(numStyleElementsBeforeRender);
-        expect(getComputedStyle(document.querySelector('.webchat__upload-button--file-input')).opacity).toBe('0');
 
         // THEN: Web Chat shows the send box with its styles.
         await host.snapshot('local');
diff --git a/__tests__/html2/strictMode/unmount.styles.html b/__tests__/html2/strictMode/unmount.styles.html
index b2b97545f0..755cd6b01c 100644
--- a/__tests__/html2/strictMode/unmount.styles.html
+++ b/__tests__/html2/strictMode/unmount.styles.html
@@ -46,9 +46,8 @@
 
         await pageConditions.uiConnected();
 
-        // THEN: Web Chat has its styles: only they hide the file input of the upload button.
+        // THEN: Web Chat added its <style> elements.
         expect(getNumStyleElements()).toBeGreaterThan(numStyleElementsBeforeRender);
-        expect(getComputedStyle(document.querySelector('.webchat__upload-button--file-input')).opacity).toBe('0');
 
         // THEN: Web Chat shows the send box with its styles.
         await host.snapshot('local');

From c129fe13b8207905998a6c59fe9bcb94af7cbef2 Mon Sep 17 00:00:00 2001
From: Eugene Olonov <eugeneolonov@microsoft.com>
Date: Thu, 12 Nov 2026 12:19:24 -0800
Subject: [PATCH 4/4] Add the changelog fragment

---
 .changelog/6047-fix-activity-styles.md | 3 +++
 1 file changed, 3 insertions(+)
 create mode 100644 .changelog/6047-fix-activity-styles.md

diff --git a/.changelog/6047-fix-activity-styles.md b/.changelog/6047-fix-activity-styles.md
new file mode 100644
index 0000000000..0655eaa750
--- /dev/null
+++ b/.changelog/6047-fix-activity-styles.md
@@ -0,0 +1,3 @@
+### Fixed
+
+- Fixed styles lost after a React 19.2 `<Activity>` hides and shows Web Chat, in PR [#6047](https://github.com/microsoft/BotFramework-WebChat/pull/6047), by [@OEvgeny](https://github.com/OEvgeny)