Hey everyone,
Upgrading to Tailwind CSS v4 brings massive speed improvements, but the new Rust-powered Oxide engine fundamentally changes how CSS scoping works.
If your terminal is suddenly throwing <code>Cannot apply unknown utility class</code> errors, or if your <code>@apply</code> directives are suddenly failing, you aren’t alone. It’s a known consequence of how version 4.0 handles file-level scope.
We just published a highly technical, zero-fluff guide to get your build passing again:
<a href="https://beyondit.blog/blogs/tailwind-v4-migration-guide" target="_blank" rel="noopener nofollow">Read the Tailwind v4 Remediation Guide on Beyond IT →</a>
What you’ll learn to fix in under 3 minutes:
<ul>
<li>Proper use of the new <code>@reference</code> directive to restore theme context in isolated files.</li>
<li>Framework-specific remediation for Next.js 15, Blazor, and preventing OOM crashes in Vue/Svelte.</li>
<li>The <code>.gitignore</code> Gotcha: How to fix the bug where Tailwind silently ignores your <code>node_modules</code> and UI libraries.</li>
<li>How to easily silence <code>css(unknownAtRules)</code> warnings in VS Code.</li>
</ul>
Stop fighting the compiler and get back to building.
Cheers,
The Beyond IT Team <a href="http://beyondit.blog" target="_blank" rel="noopener nofollow">beyondit.blog</a>

Beyondit.Blog

Tailwind CSS v4's new Rust-powered Oxide engine changes how CSS scoping works, causing `Cannot apply unknown utility class` errors and broken `@apply` directives. A remediation guide covers fixes including the new `@reference` directive for restoring theme context, framework-specific solutions for Next.js 15, Blazor, and Vue/Svelte OOM crashes, a `.gitignore` gotcha that causes Tailwind to silently ignore node_modules and UI libraries, and how to suppress `css(unknownAtRules)` warnings in VS Code.

Fixing the "Unknown Utility Class" error in Tailwind v4