Found it — the culprit is this line: ```css @source "../node_modules"; ``` **Root cause:** In Tailwind v4, `@source` tells the Oxide engine to scan those files for class names to generate. Pointing it at the entire `node_modules` directory makes it scan *every* JS/TS/HTML file in every package you've installed — including packages that have nothing to do with your UI. Any string in any of those files that happens to look like a valid Tailwind utility (`text-sm`, `flex`, `p-4`, etc.) gets generated into your CSS. That's almost certainly your jump from 4KB to 80KB+. You don't need to scan `node_modules` at all — shadcn-ui components aren't styled by scanning the library's source; they're **copied into your own project** (usually `src/components/ui/`), so Tailwind already picks them up when it scans your app's source files. ### Fix Remove the broad `@source` directive entirely: ```css @import "tailwindcss"; /* Remove this line: */ /* @source "../node_modules"; */ ``` If your `@import "tailwindcss";` is at the root of your CSS and your `app.css` lives inside `src/`, Tailwind v4's automatic content detection should already pick up everything under your project root (excluding `.gitignore`d paths like `node_modules`, `dist`, etc. by default). You likely don't need any manual `@source` directive at all. **Only add `@source` back if:** - You have shadcn/ui or other component files living *outside* the default scan root (e.g., a monorepo package), in which case scope it precisely: ```css @source "../../packages/ui-components/**/*.{ts,tsx}"; ``` - Never point `@source` at `node_modules` as a whole — if you truly need one specific package's compiled output scanned (rare), target the exact subpath, e.g. `@source "../node_modules/some-specific-package/dist";`. ### Verify ```bash npm run build ``` Check the new CSS file size — it should drop back down near your original ~4KB (plus whatever shadcn-ui components you're actually using). Do a quick visual pass on the pages using shadcn-ui components to confirm nothing broke, since shadcn relies on CSS variables (`--background`, `--primary`, etc.) defined in your `@theme` block — those aren't affected by this fix, just the utility-class bloat. If size is still high after removing that line, the next place I'd check is whether your `@theme` block has leftover unused CSS variables from the v3→v4 migration — happy to take a look at that file if you want a second pass.