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Cannot apply unknown utility class <class>

Not confirmed yet · posted

Cause

@apply resolves only utilities its stylesheet's theme defines: v3 JS-config theme values aren't loaded in v4, and CSS modules or component styles have no theme.

Fix

risk: low

/* CSS module or Vue/Svelte <style>: borrow the main stylesheet's theme (emits no CSS) */@reference "../app.css";        /* or @reference "tailwindcss"; for the default theme *//* main CSS: v3 theme.extend values become theme variables */@theme { --color-primary: #4f46e5; }/* v3 @layer components classes used in @apply become utilities */@utility card { padding: 1rem; }

Don’t try

@import "tailwindcss" inside each CSS module or component <style> — duplicates the framework's CSS into every bundle; @reference gives @apply the theme without emitting CSS.

keep theme.extend in tailwind.config.js and expect v4 to read it — v4 no longer auto-detects JS configs; add @config "./tailwind.config.js" to the CSS or move the values to @theme.

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