diff --git a/frontend/postcss.config.js b/frontend/postcss.config.js
index 2e7af2b..780e822 100644
--- a/frontend/postcss.config.js
+++ b/frontend/postcss.config.js
@@ -1,6 +1,29 @@
-export default {
-  plugins: {
-    tailwindcss: {},
-    autoprefixer: {},
+import autoprefixer from 'autoprefixer'
+import tailwindcss from 'tailwindcss'
+
+// Apply the same breakpoints to handwritten CSS and Tailwind utilities.
+export const inlineBreakpoints = {
+  postcssPlugin: 'inline-breakpoints',
+  OnceExit (root) {
+    const queries = []
+    root.walkAtRules ('media', query => {
+      if (/\b(?:min|max)-width\s*:/.test (query.params))
+        queries.push (query)
+    })
+    for (const query of queries) {
+      const vertical = query.cloneAfter ({
+        params: query.params.replace (/\b(min|max)-width(?=\s*:)/g, '$1-height') })
+      for (const [branch, scope] of [
+          [query, ':where(html:not(:lang(mn-Mong)))'],
+          [vertical, ':where(html:lang(mn-Mong))']]) {
+        branch.walkRules (rule => {
+          rule.selectors = rule.selectors.map (selector => `${scope} ${selector}`)
+        })
+      }
+    }
   },
 }
+
+export default {
+  plugins: [tailwindcss (), inlineBreakpoints, autoprefixer ()],
+}
diff --git a/frontend/postcss.config.test.js b/frontend/postcss.config.test.js
new file mode 100644
index 0000000..266b407
--- /dev/null
+++ b/frontend/postcss.config.test.js
@@ -0,0 +1,52 @@
+import postcss from 'postcss'
+import tailwindcss from 'tailwindcss'
+import { describe, expect, it } from 'vitest'
+
+import { inlineBreakpoints } from './postcss.config.js'
+
+describe ('inline breakpoints', () => {
+  it ('uses height for vertical menus and width for horizontal menus', async () => {
+    const source = `
+      @media (min-width: 768px) { .menu, .account { display: flex } }
+      @media (min-width: 1024px) { .menu { font-size: 1rem } }
+      @media (max-width: 767px) { .mobile { display: block } }
+      @media (prefers-reduced-motion: reduce) { .menu { transition: none } }
+    `
+    const { css } = await postcss ([inlineBreakpoints]).process (
+        source, { from: 'menus.css' })
+    const rules = []
+    postcss.parse (css).walkRules (rule => {
+      rules.push ([rule.parent.params, rule.selector])
+    })
+
+    expect (rules).toEqual ([
+        ['(min-width: 768px)',
+          ':where(html:not(:lang(mn-Mong))) .menu, '
+          + ':where(html:not(:lang(mn-Mong))) .account'],
+        ['(min-height: 768px)',
+          ':where(html:lang(mn-Mong)) .menu, :where(html:lang(mn-Mong)) .account'],
+        ['(min-width: 1024px)', ':where(html:not(:lang(mn-Mong))) .menu'],
+        ['(min-height: 1024px)', ':where(html:lang(mn-Mong)) .menu'],
+        ['(max-width: 767px)', ':where(html:not(:lang(mn-Mong))) .mobile'],
+        ['(max-height: 767px)', ':where(html:lang(mn-Mong)) .mobile'],
+        ['(prefers-reduced-motion: reduce)', '.menu']])
+  })
+
+  it ('includes responsive utilities generated by Tailwind', async () => {
+    const { css } = await postcss ([tailwindcss ({
+        content: [{ raw: '<div class="md:hidden lg:text-base"></div>' }],
+        corePlugins: { preflight: false } }), inlineBreakpoints]).process (
+        '@tailwind utilities;', { from: 'utilities.css' })
+    const rules = []
+    postcss.parse (css).walkRules (rule => {
+      rules.push ([rule.parent.params, rule.selector])
+    })
+
+    expect (rules).toContainEqual ([
+        '(min-width: 768px)', ':where(html:not(:lang(mn-Mong))) .md\\:hidden'])
+    expect (rules).toContainEqual ([
+        '(min-height: 768px)', ':where(html:lang(mn-Mong)) .md\\:hidden'])
+    expect (rules).toContainEqual ([
+        '(min-height: 1024px)', ':where(html:lang(mn-Mong)) .lg\\:text-base'])
+  })
+})
diff --git a/frontend/src/components/ResponsiveMarqueeText.tsx b/frontend/src/components/ResponsiveMarqueeText.tsx
index 0960730..a703d2a 100644
--- a/frontend/src/components/ResponsiveMarqueeText.tsx
+++ b/frontend/src/components/ResponsiveMarqueeText.tsx
@@ -1,7 +1,9 @@
-import { useClientBehaviourSettings } from '@/lib/useClientBehaviourSettings'
-import { cn } from '@/lib/utils'
 import { useEffect, useRef, useState } from 'react'
 
+import { useClientBehaviourSettings } from '@/lib/useClientBehaviourSettings'
+import { useVerticalPreview } from '@/lib/useLocale'
+import { cn } from '@/lib/utils'
+
 import type { FC } from 'react'
 
 type Props = {
@@ -11,7 +13,7 @@ type Props = {
     title?:    string }
 
 const DESKTOP_MARQUEE_MEDIA =
-    '(min-width: 768px) and (hover: hover) and (pointer: fine) and (prefers-reduced-motion: no-preference)'
+    '(hover: hover) and (pointer: fine) and (prefers-reduced-motion: no-preference)'
 const MARQUEE_START_DELAY_MS = 1600
 const MARQUEE_END_HOLD_MS = 2400
 const MARQUEE_SCROLL_PX_PER_SECOND = 43
@@ -21,6 +23,7 @@ const MIN_MARQUEE_OVERFLOW_PX = 1
 const ResponsiveMarqueeText: FC<Props> = (
     { text, className, truncateOnMobile = false, title },
 ) => {
+  const verticalPreview = useVerticalPreview ()
   const behaviourSettings = useClientBehaviourSettings ()
   const animationMode = behaviourSettings.animation ?? 'normal'
   const outerRef = useRef<HTMLSpanElement | null> (null)
@@ -69,7 +72,8 @@ const ResponsiveMarqueeText: FC<Props> = (
     if (typeof window === 'undefined' || typeof window.matchMedia !== 'function')
       return
 
-    const media = window.matchMedia (DESKTOP_MARQUEE_MEDIA)
+    const sizeMedia = verticalPreview ? '(min-height: 768px)' : '(min-width: 768px)'
+    const media = window.matchMedia (`${ sizeMedia } and ${ DESKTOP_MARQUEE_MEDIA }`)
     const update = () => {
       setDesktopMarqueeEnabled (media.matches)
     }
@@ -80,7 +84,7 @@ const ResponsiveMarqueeText: FC<Props> = (
     return () => {
       media.removeEventListener ('change', update)
     }
-  }, [])
+  }, [verticalPreview])
 
   useEffect (() => {
     const clearScheduled = () => {
diff --git a/frontend/src/components/TopNav.tsx b/frontend/src/components/TopNav.tsx
index 7859858..4904749 100644
--- a/frontend/src/components/TopNav.tsx
+++ b/frontend/src/components/TopNav.tsx
@@ -299,21 +299,14 @@ const TopNav: FC<Props> = ({ user, locales, resolveLocaleSwitch }) => {
     let active = true
 
     const update = () => {
-      if (!(window.matchMedia ('(min-width: 768px)').matches))
+      const desktopMedia = verticalPreview ? '(min-height: 768px)' : '(min-width: 768px)'
+      if (!(window.matchMedia (desktopMedia).matches))
       {
 	setDesktop (false)
 	setDensity ('auto')
 	return
       }
 
-      if (verticalPreview)
-      {
-	setDesktop (true)
-	setDensity ('auto')
-	measure (moreVsbl ? -1 : activeIdx)
-	return
-      }
-
       // Measure the same desktop elements while the mobile layout is active.
       layout.setAttribute ('data-measuring', '')
       const previousDensity = layout.getAttribute ('data-density') ?? 'auto'
@@ -324,16 +317,25 @@ const TopNav: FC<Props> = ({ user, locales, resolveLocaleSwitch }) => {
 	  {
 	    layout.setAttribute ('data-density', candidate)
 	    const style = getComputedStyle (bar)
-	    const primaryWidth = Math.max (
-		primary.getBoundingClientRect ().width, primary.scrollWidth)
-	    const accountWidth =
+	    const primarySize =
+		verticalPreview
+		? Math.max (primary.getBoundingClientRect ().height, primary.scrollHeight)
+		: Math.max (primary.getBoundingClientRect ().width, primary.scrollWidth)
+	    const accountSize =
 		account == null
 		? 0
-		: Math.max (account.getBoundingClientRect ().width, account.scrollWidth)
-	    const required = primaryWidth + accountWidth
-		+ parseFloat (style.paddingLeft) + parseFloat (style.paddingRight)
-		+ (account == null ? 0 : parseFloat (style.columnGap))
-	    if (Math.ceil (required) <= bar.clientWidth)
+		: (verticalPreview
+		   ? Math.max (account.getBoundingClientRect ().height, account.scrollHeight)
+		   : Math.max (account.getBoundingClientRect ().width, account.scrollWidth))
+	    const padding =
+		verticalPreview
+		? parseFloat (style.paddingTop) + parseFloat (style.paddingBottom)
+		: parseFloat (style.paddingLeft) + parseFloat (style.paddingRight)
+	    const gap = verticalPreview ? style.rowGap : style.columnGap
+	    const required = primarySize + accountSize + padding
+		+ (account == null ? 0 : parseFloat (gap))
+	    const available = verticalPreview ? bar.clientHeight : bar.clientWidth
+	    if (Math.ceil (required) <= available)
 	      return candidate
 	  }
 	  return null
diff --git a/frontend/src/index.css b/frontend/src/index.css
index fd135b7..084d6b0 100644
--- a/frontend/src/index.css
+++ b/frontend/src/index.css
@@ -1355,6 +1355,16 @@ html:lang(mn-Mong) .inheritance-dialogue-fields > button
     height: auto;
   }
 
+  [data-vertical-preview] .top-nav-layout[data-measuring] .top-nav-primary,
+  [data-vertical-preview] .top-nav-layout[data-measuring] .top-nav-desktop-menu,
+  [data-vertical-preview] .top-nav-layout[data-measuring] .top-nav-account
+  {
+    flex: 0 0 auto;
+    width: 100%;
+    height: max-content;
+    max-height: none;
+  }
+
   [data-vertical-preview] .top-nav-desktop-menu > div:not(.top-nav-highlight)
   {
     width: 100%;