Why it matters
Tailwind v4 is configured in CSS. A JavaScript config is only loaded when a stylesheet references it with @config; otherwise its theme, plugins and darkMode are ignored and every class it defined produces no CSS.
How to fix it
Move the theme into @theme { … } in your CSS entry (preferred), or add @config "./tailwind.config.ts"; right after @import "tailwindcss";. Delete the JS file once migrated.
Example
@import "tailwindcss";
@theme {
--color-brand: oklch(0.62 0.19 272);
--font-display: "Inter Display", sans-serif;
}References
More lint rules
void lint reports 67 rules in this category. Static source checks with no browser: Tailwind v4 silent failures, Next.js 16 API traps, React render-body bugs, accessibility markup, SEO files and motion hygiene.
tw-unknown-classClass looks like a Tailwind utility but compiles to no CSStw-v3-arbitrary-var`utility-[--var]` is Tailwind v3 syntax; v4 needs `utility-(--var)`tw-dark-variant-os`dark:` follows the OS, but the app toggles themes with a class/attributetw-v3-renamedUtility whose meaning changed between Tailwind v3 and v4tw-important-soupMany `!important` utilities in one filetw-arbitrary-sprawlMany arbitrary colors / pixel values bypass the design tokenspage-level-use-client`"use client"` at the top of a page or layoutheavy-importHeavy dependency imported into client code