Add new FullPage component

Signed-off-by: Charles de Dreuille <charles.dedreuille@gmail.com>

.storybook/preview.tsx

@@ -5,7 +5,7 @@ import addonLinks from '@storybook/addon-links';
 import { definePreview } from '@storybook/react-vite';
 import { useEffect } from 'react';
 import { TestApiProvider } from '@backstage/test-utils';
-import { Content, AlertDisplay } from '@backstage/core-components';
+import { AlertDisplay } from '@backstage/core-components';
 import { apis } from './support/apis';
 import { useGlobals } from 'storybook/preview-api';
 import { UnifiedThemeProvider, themes } from '@backstage/theme';
@@ -146,9 +146,7 @@ export default definePreview({
           {/* @ts-ignore */}
           <TestApiProvider apis={apis}>
             <AlertDisplay />
-            <Content>
-              <Story />
-            </Content>
+            <Story />
           </TestApiProvider>
         </UnifiedThemeProvider>
       );

packages/ui/src/components/FullPage/FullPage.module.css

@@ -0,0 +1,24 @@
+/*
+ * Copyright 2025 The Backstage Authors
+ *
+ * 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.
+ */
+
+@layer tokens, base, components, utilities;
+
+@layer components {
+  .bui-FullPage {
+    height: calc(100dvh - var(--bui-header-height, 0px));
+    overflow-y: auto;
+  }
+}

packages/ui/src/components/FullPage/FullPage.stories.tsx

@@ -0,0 +1,110 @@
+/*
+ * Copyright 2025 The Backstage Authors
+ *
+ * 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.
+ */
+
+import preview from '../../../../../.storybook/preview';
+import type { StoryFn } from '@storybook/react-vite';
+import { FullPage } from './FullPage';
+import { Header } from '../Header';
+import { Container } from '../Container';
+import { Text } from '../Text';
+import type { HeaderTab } from '../Header/types';
+import { MemoryRouter } from 'react-router-dom';
+
+const meta = preview.meta({
+  title: 'Backstage UI/FullPage',
+  component: FullPage,
+  parameters: {
+    layout: 'fullscreen',
+  },
+});
+
+const withRouter = (Story: StoryFn) => (
+  <MemoryRouter>
+    <Story />
+  </MemoryRouter>
+);
+
+const tabs: HeaderTab[] = [
+  { id: 'overview', label: 'Overview', href: '/overview' },
+  { id: 'checks', label: 'Checks', href: '/checks' },
+  { id: 'tracks', label: 'Tracks', href: '/tracks' },
+  { id: 'campaigns', label: 'Campaigns', href: '/campaigns' },
+];
+
+const paragraphs = Array.from({ length: 20 }, (_, i) => (
+  <Text as="p" key={i}>
+    Lorem ipsum dolor sit amet consectetur adipisicing elit. Quisquam, quos.
+    Pellentesque habitant morbi tristique senectus et netus et malesuada fames
+    ac turpis egestas. Sed do eiusmod tempor incididunt ut labore et dolore
+    magna aliqua.
+  </Text>
+));
+
+export const Default = meta.story({
+  decorators: [withRouter],
+  render: () => (
+    <>
+      <Header title="My Plugin" />
+      <FullPage style={{ backgroundColor: '#c3f0ff' }}>
+        <Container>
+          <Text as="p">
+            This content fills the remaining viewport height below the Header.
+          </Text>
+        </Container>
+      </FullPage>
+    </>
+  ),
+});
+
+export const WithScrollableContent = meta.story({
+  decorators: [withRouter],
+  render: () => (
+    <>
+      <Header title="My Plugin" />
+      <FullPage>
+        <Container>
+          <Text as="h2" variant="title-medium">
+            Scrollable Content
+          </Text>
+          <Text as="p">
+            The content below scrolls independently while the Header stays
+            pinned at the top.
+          </Text>
+          {paragraphs}
+        </Container>
+      </FullPage>
+    </>
+  ),
+});
+
+export const WithTabs = meta.story({
+  decorators: [withRouter],
+  render: () => (
+    <>
+      <Header title="My Plugin" tabs={tabs} />
+      <FullPage>
+        <Container>
+          <Text as="p">
+            The FullPage height adjusts automatically when the Header includes
+            tabs, thanks to the ResizeObserver measuring the Header's actual
+            height.
+          </Text>
+          {paragraphs}
+        </Container>
+      </FullPage>
+    </>
+  ),
+});

packages/ui/src/components/FullPage/FullPage.tsx

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2025 The Backstage Authors
+ *
+ * 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.
+ */
+
+import { forwardRef } from 'react';
+import type { FullPageProps } from './types';
+import { useStyles } from '../../hooks/useStyles';
+import { FullPageDefinition } from './definition';
+import styles from './FullPage.module.css';
+import clsx from 'clsx';
+
+/**
+ * A component that fills the remaining viewport height below the Header.
+ *
+ * The FullPage component consumes the `--bui-header-height` CSS custom property
+ * set by the Header component to calculate its height as
+ * `calc(100dvh - var(--bui-header-height, 0px))`. Content inside the FullPage
+ * scrolls independently while the Header stays visible.
+ *
+ * @public
+ */
+export const FullPage = forwardRef<HTMLElement, FullPageProps>((props, ref) => {
+  const { classNames, cleanedProps } = useStyles(FullPageDefinition, props);
+  const { className, ...rest } = cleanedProps;
+
+  return (
+    <main
+      ref={ref}
+      className={clsx(classNames.root, styles[classNames.root], className)}
+      {...rest}
+    />
+  );
+});

packages/ui/src/components/FullPage/definition.ts

@@ -0,0 +1,27 @@
+/*
+ * Copyright 2025 The Backstage Authors
+ *
+ * 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.
+ */
+
+import type { ComponentDefinition } from '../../types';
+
+/**
+ * Component definition for FullPage
+ * @public
+ */
+export const FullPageDefinition = {
+  classNames: {
+    root: 'bui-FullPage',
+  },
+} as const satisfies ComponentDefinition;

packages/ui/src/components/FullPage/index.tsx

@@ -0,0 +1,19 @@
+/*
+ * Copyright 2025 The Backstage Authors
+ *
+ * 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.
+ */
+
+export { FullPage } from './FullPage';
+export { FullPageDefinition } from './definition';
+export type { FullPageProps } from './types';

packages/ui/src/components/FullPage/types.ts

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2025 The Backstage Authors
+ *
+ * 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.
+ */
+
+/**
+ * Props for the FullPage component.
+ *
+ * @public
+ */
+export interface FullPageProps extends React.ComponentPropsWithoutRef<'main'> {}

packages/ui/src/components/Header/Header.module.css

@@ -17,9 +17,11 @@
 @layer tokens, base, components, utilities;
 
 @layer components {
-  .bui-HeaderToolbar {
-    margin-bottom: var(--bui-space-6);
+  .bui-Header {
+    display: block;
+  }
 
+  .bui-HeaderToolbar {
     &::before {
       content: '';
       position: absolute;
@@ -30,10 +32,6 @@
       background-color: var(--bui-bg-neutral-0);
       z-index: 0;
     }
-
-    &[data-has-tabs='true'] {
-      margin-bottom: 0;
-    }
   }
 
   .bui-HeaderToolbarWrapper {

packages/ui/src/components/Header/Header.tsx

@@ -20,6 +20,7 @@ import { Tabs, TabList, Tab } from '../Tabs';
 import { useStyles } from '../../hooks/useStyles';
 import { HeaderDefinition } from './definition';
 import { type NavigateOptions } from 'react-router-dom';
+import { useRef, useEffect } from 'react';
 import styles from './Header.module.css';
 import clsx from 'clsx';
 
@@ -47,9 +48,35 @@ export const Header = (props: HeaderProps) => {
   } = cleanedProps;
 
   const hasTabs = tabs && tabs.length > 0;
+  const headerRef = useRef<HTMLElement>(null);
+
+  useEffect(() => {
+    const el = headerRef.current;
+    if (!el) return undefined;
+
+    const updateHeight = () => {
+      const height = el.offsetHeight;
+      document.documentElement.style.setProperty(
+        '--bui-header-height',
+        `${height}px`,
+      );
+    };
+
+    const observer = new ResizeObserver(updateHeight);
+    observer.observe(el);
+    updateHeight();
+
+    return () => {
+      observer.disconnect();
+      document.documentElement.style.removeProperty('--bui-header-height');
+    };
+  }, []);
 
   return (
-    <>
+    <header
+      ref={headerRef}
+      className={clsx(classNames.root, styles[classNames.root])}
+    >
       <HeaderToolbar
         icon={icon}
         title={title}
@@ -81,6 +108,6 @@ export const Header = (props: HeaderProps) => {
           </Tabs>
         </div>
       )}
-    </>
+    </header>
   );
 };

packages/ui/src/components/Header/definition.ts

@@ -22,6 +22,7 @@ import type { ComponentDefinition } from '../../types';
  */
 export const HeaderDefinition = {
   classNames: {
+    root: 'bui-Header',
     toolbar: 'bui-HeaderToolbar',
     toolbarWrapper: 'bui-HeaderToolbarWrapper',
     toolbarContent: 'bui-HeaderToolbarContent',

packages/ui/src/index.ts

@@ -25,6 +25,7 @@ export * from './components/Box';
 export * from './components/Grid';
 export * from './components/Flex';
 export * from './components/Container';
+export * from './components/FullPage';
 
 // UI components
 export * from './components/Accordion';