@@ -2,6 +2,7 @@
 
 import { useEffect, useRef, useState } from 'react'
 import {
+  cn,
   Loader,
   Modal,
   ModalClose,
@@ -22,6 +23,7 @@ import { getEnv, isFalsy } from '@/lib/core/config/env'
 import { isSsoEnabled } from '@/lib/core/config/env-flags'
 import { captureClientEvent } from '@/lib/posthog/client'
 import type { PostHogEventMap } from '@/lib/posthog/events'
+import colorMixFallbacks from '@/app/(landing)/components/shared/color-mix-fallbacks/color-mix-fallbacks.module.css'
 import { getBrandConfig } from '@/ee/whitelabeling'
 
 const logger = createLogger('AuthModal')
@@ -196,7 +198,12 @@ export function AuthModal({ children, defaultView = 'login', source }: AuthModal
                   className='h-[22px] w-auto shrink-0 object-contain'
                 />
                 <div className='flex flex-col gap-1 text-left'>
-                  <p className='text-[22px] text-[color-mix(in_srgb,var(--text-muted)_60%,transparent)] leading-[125%] tracking-[0.02em]'>
+                  <p
+                    className={cn(
+                      'text-[22px] leading-[125%] tracking-[0.02em]',
+                      colorMixFallbacks.mutedText60
+                    )}
+                  >
                     Start building.
                   </p>
                   <h2 className='text-[22px] text-[var(--text-primary)] leading-[110%] tracking-[-0.02em]'>
 
@@ -38,6 +38,7 @@ import {
   TYPE_MS_PER_ATOM,
   WORKFLOW_FOCUS_SCALE,
 } from '@/app/(landing)/components/hero/components/hero-visual/workflow-data'
+import colorMixFallbacks from '@/app/(landing)/components/shared/color-mix-fallbacks/color-mix-fallbacks.module.css'
 
 /**
  * Animated hero visual - the only client island in the hero, decorative and
@@ -299,7 +300,7 @@ const SEND_BUTTON_INK = {
  */
 const LANDING_LOADER_INK = {
   '--tl-grad-inner': 'var(--text-body)',
-  '--tl-grad-outer': 'color-mix(in srgb, var(--text-body) 76%, #fff)',
+  '--tl-grad-outer': 'var(--thinking-loader-outer)',
   '--tl-glow': 'transparent',
 } as CSSProperties
 
@@ -1144,6 +1145,7 @@ export function HeroVisual() {
             // layer, so the slide + dock read as smooth sub-pixel motion instead of
             // jittering as the position pixel-snaps each frame.
             'pointer-events-none absolute top-0 left-0 z-20 transform-gpu transition-opacity duration-300 will-change-transform [transition-timing-function:cubic-bezier(0.23,1,0.32,1)]',
+            colorMixFallbacks.loaderOuter,
             loaderFading ? 'opacity-0' : 'opacity-100'
           )}
           style={{ transformOrigin: '0 0' }}
 
@@ -3,6 +3,7 @@
 import { type CSSProperties, type ReactNode, useState } from 'react'
 import { cn } from '@sim/emcn'
 import { ThinkingLoader } from '@/components/ui'
+import colorMixFallbacks from '@/app/(landing)/components/shared/color-mix-fallbacks/color-mix-fallbacks.module.css'
 
 interface LogoMarkProps {
   /** Server-rendered Sim wordmark, shown by default. */
@@ -18,7 +19,7 @@ interface LogoMarkProps {
  */
 const LOADER_INK = {
   '--tl-grad-inner': 'var(--text-body)',
-  '--tl-grad-outer': 'color-mix(in srgb, var(--text-body) 76%, #fff)',
+  '--tl-grad-outer': 'var(--thinking-loader-outer)',
   '--tl-glow': 'transparent',
 } as CSSProperties
 
@@ -35,7 +36,7 @@ export function LogoMark({ children }: LogoMarkProps) {
 
   return (
     <span
-      className='relative inline-flex items-center'
+      className={cn('relative inline-flex items-center', colorMixFallbacks.loaderOuter)}
       // Transform + its transition are inline on purpose: Tailwind's
       // `transition-transform` utility (its var-based transform composition)
       // prevents the scale from applying on this element, so the transition is
 
@@ -10,6 +10,7 @@ import {
   NAVBAR_GLASS_SURFACE,
   useNavbarFrost,
 } from '@/app/(landing)/components/navbar/components/navbar-shell'
+import colorMixFallbacks from '@/app/(landing)/components/shared/color-mix-fallbacks/color-mix-fallbacks.module.css'
 import { DEMO_HREF, SIGNUP_HREF } from '@/app/(landing)/constants'
 
 /**
@@ -92,7 +93,10 @@ export function MobileNav({ stars }: MobileNavProps) {
           aria-hidden='true'
           tabIndex={-1}
           onClick={() => setOpen(false)}
-          className='fixed inset-0 top-full z-40 cursor-default bg-[color-mix(in_srgb,var(--text-primary)_8%,transparent)]'
+          className={cn(
+            'fixed inset-0 top-full z-40 cursor-default',
+            colorMixFallbacks.mobileBackdrop
+          )}
         />
       ) : null}
 
 
@@ -26,7 +26,7 @@ const ROW_CLASS =
 const TITLE_CLASS = 'truncate text-[14px] text-[var(--text-body)]'
 const DESC_CLASS = 'text-[12px] text-[var(--text-muted)] leading-snug'
 const ARROW_CLASS =
-  'size-4 flex-shrink-0 -translate-x-1 text-[var(--text-icon)] opacity-0 transition-all group-hover/item:translate-x-0 group-hover/item:opacity-100 group-focus-visible/item:translate-x-0 group-focus-visible/item:opacity-100 motion-reduce:transition-none'
+  'size-4 flex-shrink-0 -translate-x-1 text-[var(--text-icon)] opacity-0 transition-[opacity,transform] group-hover/item:translate-x-0 group-hover/item:opacity-100 group-focus-visible/item:translate-x-0 group-focus-visible/item:opacity-100 motion-reduce:transition-none'
 
 export function NavMenuItem({ item, onSelect }: NavMenuItemProps) {
   const { title, description, href, external } = item
 
@@ -3,15 +3,15 @@
 import type { ReactNode } from 'react'
 import { createContext, use, useEffect, useMemo, useRef, useState } from 'react'
 import { cn } from '@sim/emcn'
+import colorMixFallbacks from '@/app/(landing)/components/shared/color-mix-fallbacks/color-mix-fallbacks.module.css'
 
 /**
  * Frosted near-white surface for the scrolled bar - `--bg` at 92% + a strong 40px
  * blur, edge to edge. Exported as the single source of truth so the mobile
  * dropdown sheet ({@link MobileNav}) wears the exact same glass as the bar and the
  * two can never drift.
  */
-export const NAVBAR_GLASS_SURFACE =
-  'bg-[color-mix(in_srgb,var(--bg)_92%,transparent)] backdrop-blur-2xl'
+export const NAVBAR_GLASS_SURFACE = cn(colorMixFallbacks.navbarGlass, 'backdrop-blur-2xl')
 
 interface NavbarFrostContextValue {
   /**
 
@@ -1,6 +1,7 @@
 import type { ReactNode } from 'react'
 import { cn } from '@sim/emcn'
 import styles from '@/app/(landing)/components/shared/code-window-graphic/code-window-graphic.module.css'
+import colorMixFallbacks from '@/app/(landing)/components/shared/color-mix-fallbacks/color-mix-fallbacks.module.css'
 import { FeatureGraphicShell } from '@/app/(landing)/enterprise/components/feature-graphics'
 
 /** One inline run of code text inside a {@link CodeWindowGraphic} line. */
@@ -40,7 +41,7 @@ const SEGMENT_TONE_CLASS = {
 } as const
 
 /** Shared hairline ink for the window outline, header rule, and icon box. */
-const OUTLINE_INK = 'border-[color:color-mix(in_srgb,var(--text-muted-inverse)_45%,transparent)]'
+const OUTLINE_INK = colorMixFallbacks.inverseBorder45
 
 /**
  * The dark-tile outlined editor window shared by the platform pages' "from
 
@@ -0,0 +1,115 @@
+.navbarGlass {
+  background-color: var(--bg);
+}
+
+.mobileBackdrop {
+  background-color: var(--text-primary);
+  opacity: 0.08;
+}
+
+.mutedText60 {
+  color: var(--text-muted);
+}
+
+.loaderOuter {
+  --thinking-loader-outer: var(--text-body);
+}
+
+.inverseBorder45 {
+  border-color: var(--text-muted-inverse);
+}
+
+.inverseBackground45 {
+  background-color: var(--text-muted-inverse);
+}
+
+.mutedBackground35 {
+  background-color: var(--text-muted);
+}
+
+.mutedBorder60 {
+  border-color: var(--text-muted);
+}
+
+.inverseBorder22 {
+  border-color: var(--text-muted-inverse);
+}
+
+.inverseBorder35 {
+  border-color: var(--text-muted-inverse);
+}
+
+.inverseBorder70 {
+  border-color: var(--text-muted-inverse);
+}
+
+.mutedStroke35 {
+  stroke: var(--text-muted);
+}
+
+.inverseStroke28 {
+  stroke: var(--text-muted-inverse);
+}
+
+.inverseStroke45 {
+  stroke: var(--text-muted-inverse);
+}
+
+@supports (color: color-mix(in srgb, red, blue)) {
+  .navbarGlass {
+    background-color: color-mix(in srgb, var(--bg) 92%, transparent);
+  }
+
+  .mobileBackdrop {
+    background-color: color-mix(in srgb, var(--text-primary) 8%, transparent);
+    opacity: 1;
+  }
+
+  .mutedText60 {
+    color: color-mix(in srgb, var(--text-muted) 60%, transparent);
+  }
+
+  .loaderOuter {
+    --thinking-loader-outer: color-mix(in srgb, var(--text-body) 76%, var(--white));
+  }
+
+  .inverseBorder45 {
+    border-color: color-mix(in srgb, var(--text-muted-inverse) 45%, transparent);
+  }
+
+  .inverseBackground45 {
+    background-color: color-mix(in srgb, var(--text-muted-inverse) 45%, transparent);
+  }
+
+  .mutedBackground35 {
+    background-color: color-mix(in srgb, var(--text-muted) 35%, transparent);
+  }
+
+  .mutedBorder60 {
+    border-color: color-mix(in srgb, var(--text-muted) 60%, transparent);
+  }
+
+  .inverseBorder22 {
+    border-color: color-mix(in srgb, var(--text-muted-inverse) 22%, transparent);
+  }
+
+  .inverseBorder35 {
+    border-color: color-mix(in srgb, var(--text-muted-inverse) 35%, transparent);
+  }
+
+  .inverseBorder70 {
+    border-color: color-mix(in srgb, var(--text-muted-inverse) 70%, transparent);
+  }
+
+  .mutedStroke35 {
+    stroke: color-mix(in srgb, var(--text-muted) 35%, transparent);
+  }
+
+  .inverseStroke28 {
+    stroke: color-mix(in srgb, var(--text-muted-inverse) 28%, transparent);
+  }
+
+  .inverseStroke45 {
+    stroke: color-mix(in srgb, var(--text-muted-inverse) 45%, transparent);
+  }
+}
@@ -1,10 +1,11 @@
 'use client'
 
-import { type CSSProperties, useEffect, useRef, useState } from 'react'
+import { type CSSProperties, type RefObject, useEffect, useRef, useState } from 'react'
 import { chipBorderShadowRing, cn } from '@sim/emcn'
 import dynamic from 'next/dynamic'
 import { preconnect } from 'react-dom'
 import { DemoForm, type DemoLead } from '@/app/(landing)/demo/components/demo-form'
+import { applyLegacyInertFallback } from '@/app/(landing)/demo/components/legacy-inert-fallback'
 
 const importScheduler = () => import('@/app/(landing)/demo/components/demo-scheduler')
 
@@ -32,6 +33,14 @@ const DemoScheduler = dynamic(() => importScheduler().then((m) => m.DemoSchedule
   loading: () => null,
 })
 
+function useLegacyInertFallback(ref: RefObject<HTMLDivElement | null>, inert: boolean) {
+  useEffect(() => {
+    const node = ref.current
+    if (!inert || !node || 'inert' in HTMLElement.prototype) return
+    return applyLegacyInertFallback(node)
+  }, [inert, ref])
+}
+
 interface DemoBookingProps {
   /** Layout/placement classes (grid cell). Never chrome. */
   className?: string
@@ -59,8 +68,13 @@ export function DemoBooking({ className }: DemoBookingProps) {
   const [lead, setLead] = useState<DemoLead | null>(null)
   const [formHeight, setFormHeight] = useState<number>()
   const formRef = useRef<HTMLDivElement>(null)
+  const formPanelRef = useRef<HTMLDivElement>(null)
+  const schedulerPanelRef = useRef<HTMLDivElement>(null)
   const showScheduler = lead !== null
 
+  useLegacyInertFallback(formPanelRef, showScheduler)
+  useLegacyInertFallback(schedulerPanelRef, !showScheduler)
+
   useEffect(() => {
     const node = formRef.current
     if (!node) return
@@ -87,6 +101,7 @@ export function DemoBooking({ className }: DemoBookingProps) {
         style={{ transform: showScheduler ? 'translateX(-100%)' : undefined }}
       >
         <div
+          ref={formPanelRef}
           className='w-full min-w-0 shrink-0'
           inert={showScheduler}
           onFocusCapture={() => void preloadScheduler()}
@@ -95,7 +110,11 @@ export function DemoBooking({ className }: DemoBookingProps) {
             <DemoForm onComplete={setLead} />
           </div>
         </div>
-        <div className='h-full w-full min-w-0 shrink-0' inert={!showScheduler}>
+        <div
+          ref={schedulerPanelRef}
+          className='h-full w-full min-w-0 shrink-0'
+          inert={!showScheduler}
+        >
           {lead ? <DemoScheduler lead={lead} /> : null}
         </div>
       </div>
 
@@ -0,0 +1,53 @@
+/**
+ * @vitest-environment jsdom
+ */
+import { describe, expect, it } from 'vitest'
+import { applyLegacyInertFallback } from '@/app/(landing)/demo/components/legacy-inert-fallback'
+
+describe('applyLegacyInertFallback', () => {
+  it('removes descendants from interaction and restores their exact prior state', () => {
+    const panel = document.createElement('div')
+    panel.setAttribute('aria-hidden', 'false')
+    panel.style.pointerEvents = 'auto'
+    panel.innerHTML = `
+      <button>Continue</button>
+      <a href="/demo" tabindex="2">Demo</a>
+      <input disabled />
+    `
+
+    const button = panel.querySelector('button')
+    const link = panel.querySelector('a')
+    const disabledInput = panel.querySelector('input')
+    const restore = applyLegacyInertFallback(panel)
+
+    expect(panel.getAttribute('aria-hidden')).toBe('true')
+    expect(panel.style.pointerEvents).toBe('none')
+    expect(button?.getAttribute('tabindex')).toBe('-1')
+    expect(link?.getAttribute('tabindex')).toBe('-1')
+    expect(disabledInput?.getAttribute('tabindex')).toBeNull()
+
+    restore()
+
+    expect(panel.getAttribute('aria-hidden')).toBe('false')
+    expect(panel.style.pointerEvents).toBe('auto')
+    expect(button?.getAttribute('tabindex')).toBeNull()
+    expect(link?.getAttribute('tabindex')).toBe('2')
+  })
+
+  it('moves focus out of a panel before hiding it', () => {
+    const panel = document.createElement('div')
+    const button = document.createElement('button')
+    panel.append(button)
+    document.body.append(panel)
+    button.focus()
+
+    expect(document.activeElement).toBe(button)
+
+    const restore = applyLegacyInertFallback(panel)
+
+    expect(document.activeElement).not.toBe(button)
+
+    restore()
+    panel.remove()
+  })
+})