Fix a Website That Looks Broken in Your Browser (Run the CSS Test)

Confirm which CSS feature is failing

Open the CSS Test. It checks the core building blocks many sites rely on:

• CSS Grid and Flexbox for layout
• position: sticky for headers and sidebars
• backdrop-filter for blur and translucent panels
• :has() for advanced selectors used in modern UI kits

Keep the test open while you troubleshoot. After each change, refresh the page and rerun the CSS Test to see what changed.

Common symptoms:

• Cards overlap or stack in one narrow column
• Menus open but are off-screen
• Sticky headers scroll away
• The site looks unstyled or "half loaded"
• Blur effects are replaced by solid blocks

Fix 1: Update the browser first

Missing CSS features usually means an outdated build or a locked-down browser.

• Run the Full Browser Test and check your browser version.
• Update Chrome/Edge/Firefox via Menu > Help > About and relaunch.
• Safari updates through macOS: System Settings > General > Software Update.

If you cannot update (managed device), try another supported browser temporarily. Then continue with the fixes below for site-specific breakages.

Fix 2: Turn off compatibility modes (Edge is the usual trap)

Compatibility modes can disable modern layout behavior.

• In Edge, open edge://settings/defaultBrowser.
• Set Allow sites to be reloaded in Internet Explorer mode to Disabled.
• Remove the domain from the Internet Explorer mode pages list if present.

Reload the site and rerun the CSS Test. If Grid or :has() suddenly starts working, IE mode was the cause.

Fix 3: Disable reader/simplified views and page modifiers

Reader modes can strip styles on purpose.

• Safari: if Reader is enabled, turn it off in the address bar and reload.
• Edge: exit Immersive Reader and reload.
• If you use translation overlays or "simplify page" features, disable them for the site while testing.

Fix 4: Disable extensions that inject or rewrite CSS

Dark mode and customization extensions can break layouts by overriding variables and filters.

• Disable extensions like Dark Reader, Stylus, custom CSS injectors, and aggressive ad blockers with cosmetic filtering.
• Test in an Incognito/InPrivate window with extensions disabled.
• If the site works in private mode, re-enable extensions one by one and add a site allowlist rule for the culprit.

Fix 5: Hard refresh and clear cached site data

Sites that ship new CSS can break if you have old cached files or an outdated service worker.

1. Hard reload (Windows/Linux: Ctrl+Shift+R; macOS: Cmd+Shift+R).
2. If the layout still breaks, clear the site’s data (cookies + storage) in browser settings.
3. Sign back in and recheck the layout.

After clearing, rerun the CSS Test and reload the site once more.

Fix 6: Repair GPU compositing for blur and smooth UI

If only backdrop-filter looks wrong (no blur, solid blocks), your GPU path can be disabled.

• Run the WebGL Test. If it fails, fix hardware acceleration and GPU drivers first.
• Chrome/Edge: Settings > System and performance > Use hardware acceleration when available.
• Restart the browser and reload the site.

Some sites use GPU-accelerated effects heavily. Without acceleration, they fall back to simpler visuals or glitchy layers.

Fix 7: Rule out network filtering that blocks CSS files

Corporate proxies and DNS filters can block static asset domains (CDNs). The site loads HTML, but stylesheets fail.

• Test the site on another network (mobile hotspot).
• If the site works on the hotspot, your network is blocking required assets. Ask IT to allow the site’s CDN domains instead of disabling protection globally.

Verify the fix

Rerun the CSS Test. For most modern apps, you want at least Grid, Flexbox, sticky, and :has() to be supported. Then reload the problem site and confirm the layout is stable: menus open in the right place, headers stick, and content is readable.