UI: Add the new structure for the mobile layout

code/ui/manager/src/components/hooks/useMedia.tsx

@@ -1,19 +1,34 @@
-import { useState, useEffect } from 'react';
+import { useEffect, useState } from 'react';
 
-const useMediaQuery = (query: string) => {
-  const [matches, setMatches] = useState(false);
+export function useMediaQuery(query: string): boolean {
+  const getMatches = (queryMatch: string): boolean => {
+    // Prevents SSR issues
+    if (typeof window !== 'undefined') {
+      return window.matchMedia(queryMatch).matches;
+    }
+    return false;
+  };
+
+  const [matches, setMatches] = useState<boolean>(getMatches(query));
+
+  function handleChange() {
+    setMatches(getMatches(query));
+  }
 
   useEffect(() => {
-    const media = window.matchMedia(query);
-    if (media.matches !== matches) {
-      setMatches(media.matches);
-    }
-    const listener = () => setMatches(media.matches);
-    window.addEventListener('resize', listener);
-    return () => window.removeEventListener('resize', listener);
-  }, [matches, query]);
+    const matchMedia = window.matchMedia(query);
 
-  return matches;
-};
+    // Triggered at the first client-side load and if query changes
+    handleChange();
+
+    // Listen matchMedia
+    matchMedia.addEventListener('change', handleChange);
 
-export default useMediaQuery;
+    return () => {
+      matchMedia.removeEventListener('change', handleChange);
+    };
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [query]);
+
+  return matches;
+}

code/ui/manager/src/components/layout/Layout.stories.tsx

@@ -61,13 +61,7 @@ const meta = {
     theme: 'light',
     layout: 'fullscreen',
   },
-  decorators: [
-    (Story) => (
-      <div style={{ height: '100vh', width: '100vw' }}>
-        <Story />
-      </div>
-    ),
-  ],
+  decorators: [(Story) => <Story />],
   render: (args) => {
     const [managerLayoutState, setManagerLayoutState] = useState(args.managerLayoutState);
 

code/ui/manager/src/components/layout/Layout.tsx

@@ -2,6 +2,9 @@ import React, { useEffect, useLayoutEffect, useState } from 'react';
 import { styled } from '@storybook/theming';
 import type { API_Layout, API_ViewMode } from '@storybook/types';
 import { useDragging } from './useDragging';
+import { useMediaQuery } from '../hooks/useMedia';
+import { MobileNavigation } from '../mobile-navigation/MobileNavigation';
+import { breakpointMin600 } from '../../constants';
 
 interface InternalLayoutState {
   isDragging: boolean;
@@ -110,6 +113,9 @@ const useLayoutSyncingState = (
 };
 
 export const Layout = ({ managerLayoutState, setManagerLayoutState, ...slots }: Props) => {
+  const isDesktop = useMediaQuery(breakpointMin600);
+  const isMobile = !isDesktop;
+
   const {
     navSize,
     rightPanelWidth,
@@ -130,51 +136,70 @@ export const Layout = ({ managerLayoutState, setManagerLayoutState, ...slots }:
       panelPosition={managerLayoutState.panelPosition}
       isDragging={isDragging}
       viewMode={managerLayoutState.viewMode}
+      breakpoint={breakpointMin600}
     >
       {showPages && <PagesContainer>{slots.slotPages}</PagesContainer>}
-      <ContentContainer>{slots.slotMain}</ContentContainer>
-      <SidebarContainer>
-        <Drag ref={sidebarResizerRef} />
-        {slots.slotSidebar}
-      </SidebarContainer>
-      {showPanel && (
-        <PanelContainer position={panelPosition}>
-          <Drag
-            orientation={panelPosition === 'bottom' ? 'horizontal' : 'vertical'}
-            position={panelPosition === 'bottom' ? 'left' : 'right'}
-            ref={panelResizerRef}
-          />
-          {slots.slotPanel}
-        </PanelContainer>
+      <ContentContainer breakpoint={breakpointMin600}>{slots.slotMain}</ContentContainer>
+      {isDesktop && (
+        <>
+          <SidebarContainer>
+            <Drag ref={sidebarResizerRef} />
+            {slots.slotSidebar}
+          </SidebarContainer>
+          {showPanel && (
+            <PanelContainer position={panelPosition}>
+              <Drag
+                orientation={panelPosition === 'bottom' ? 'horizontal' : 'vertical'}
+                position={panelPosition === 'bottom' ? 'left' : 'right'}
+                ref={panelResizerRef}
+              />
+              {slots.slotPanel}
+            </PanelContainer>
+          )}
+        </>
       )}
+      {isMobile && <MobileNavigation />}
     </LayoutContainer>
   );
 };
 
-const LayoutContainer = styled.div<LayoutState>(
-  ({ navSize, rightPanelWidth, bottomPanelHeight, viewMode, panelPosition, isDragging }) => {
+const LayoutContainer = styled.div<LayoutState & { breakpoint: string }>(
+  ({
+    navSize,
+    rightPanelWidth,
+    bottomPanelHeight,
+    viewMode,
+    panelPosition,
+    isDragging,
+    breakpoint,
+  }) => {
     return {
       width: '100%',
-      height: '100vh',
-      display: 'grid',
+      height: '100svh',
       overflow: 'hidden',
-      gap: 0,
-      transition: isDragging ? null : 'all 0.2s ease-in-out', // transition when toggling panels, but not when dragging
-      gridTemplateColumns: `minmax(0, ${navSize}px) minmax(${MINIMUM_CONTENT_WIDTH_PX}px, 1fr) minmax(0, ${rightPanelWidth}px)`,
-      gridTemplateRows: `1fr ${bottomPanelHeight}px`,
-      gridTemplateAreas: (() => {
-        if (viewMode === 'docs') {
-          // remove panel in docs viewMode
-          return `"sidebar content content"
+      display: 'flex',
+      flexDirection: 'column',
+
+      [`@media ${breakpoint}`]: {
+        display: 'grid',
+        gap: 0,
+        transition: isDragging ? null : 'all 0.2s ease-in-out', // transition when toggling panels, but not when dragging
+        gridTemplateColumns: `minmax(0, ${navSize}px) minmax(${MINIMUM_CONTENT_WIDTH_PX}px, 1fr) minmax(0, ${rightPanelWidth}px)`,
+        gridTemplateRows: `1fr ${bottomPanelHeight}px`,
+        gridTemplateAreas: (() => {
+          if (viewMode === 'docs') {
+            // remove panel in docs viewMode
+            return `"sidebar content content"
                   "sidebar content content"`;
-        }
-        if (panelPosition === 'right') {
-          return `"sidebar content panel"
+          }
+          if (panelPosition === 'right') {
+            return `"sidebar content panel"
                   "sidebar content panel"`;
-        }
-        return `"sidebar content content"
+          }
+          return `"sidebar content content"
                 "sidebar panel   panel"`;
-      })(),
+        })(),
+      },
     };
   }
 );
@@ -186,11 +211,16 @@ const SidebarContainer = styled.div(({ theme }) => ({
   borderRight: `1px solid ${theme.color.border}`,
 }));
 
-const ContentContainer = styled.div(({ theme }) => ({
-  display: 'grid',
+const ContentContainer = styled.div<{ breakpoint: string }>(({ theme, breakpoint }) => ({
+  flex: 1,
   position: 'relative',
   backgroundColor: theme.background.content,
-  gridArea: 'content',
+  display: 'grid', // This is needed to make the content container fill the available space
+
+  [`@media ${breakpoint}`]: {
+    flex: 'auto',
+    gridArea: 'content',
+  },
 }));
 
 const PagesContainer = styled.div(({ theme }) => ({

code/ui/manager/src/components/mobile-navigation/MobileNavigation.tsx

@@ -0,0 +1,21 @@
+import type { FC } from 'react';
+import React from 'react';
+import { styled } from '@storybook/theming';
+
+const Container = styled.div(({ theme }) => ({
+  display: 'flex',
+  alignItems: 'center',
+  justifyContent: 'space-between',
+  bottom: 0,
+  left: 0,
+  width: '100%',
+  height: 40,
+  zIndex: 10,
+  background: theme.background.content,
+  padding: '0 6px',
+  borderTop: `1px solid ${theme.appBorderColor}`,
+}));
+
+export const MobileNavigation: FC = () => {
+  return <Container />;
+};

code/ui/manager/src/components/panel/Panel.tsx

@@ -3,7 +3,7 @@ import { Tabs, Icons, IconButton } from '@storybook/components';
 import type { State } from '@storybook/manager-api';
 import { shortcutToHumanString } from '@storybook/manager-api';
 import type { Addon_BaseType } from '@storybook/types';
-import useMediaQuery from '../hooks/useMedia';
+import { useMediaQuery } from '../hooks/useMedia';
 
 export interface SafeTabProps {
   title: Addon_BaseType['title'];

code/ui/manager/src/constants.ts

@@ -0,0 +1 @@
+export const breakpointMin600 = '(min-width: 600px)';