# Plugin styling — the `styles` capability
> Building for the redesigned **v3 UI** (`FEEDBACK_UI=v3` / `/v3`)? v3 uses `fb-*`
> design tokens and a restructured player chrome with a dedicated plugin-control
> slot. See **[plugin-v3-ui.md](plugin-v3-ui.md)** for the player-chrome contract
> plugins must follow in v3.
FeedBack serves Tailwind as a **prebuilt** stylesheet
(`static/tailwind.min.css`), never the runtime Play CDN. The CDN's on-the-fly
JIT rescanned the DOM on the main thread and dropped ~26% of frames with the 3D
highway running (feedBack-desktop#110). See **constitution Principle II**.
A prebuilt stylesheet only contains the classes the build scanner saw in **core
source at core build time**. That has a consequence for plugins:
- Core's build scans bundled plugins on disk, but **a plugin installed at
runtime** (community / NAS) was never scanned. Its classes — especially
arbitrary values like `text-[11px]`, `grid-cols-[1fr_auto]`,
`shadow-[0_0_8px_rgba(0,0,0,.5)]` — are **absent** from the served CSS, so its
UI renders unstyled.
The `styles` capability fixes this: your plugin ships its **own** compiled
stylesheet and declares it in the manifest. The frontend injects one versioned
`` into `` when your plugin activates, covering both
your screen and your settings panel.
> You only need this if you use Tailwind classes that aren't guaranteed in core —
> in practice, **any arbitrary-value class** (`w-[37px]`), or a custom class core
> doesn't ship. If you use only common core utilities (`flex`, `p-4`,
> `text-gray-300`, `bg-dark-600`), you can omit `styles` and rely on core's CSS.
## 1. Declare it in `plugin.json`
```json
{
"id": "my_plugin",
"name": "My Plugin",
"version": "1.2.0",
"screen": "screen.html",
"script": "screen.js",
"styles": "assets/plugin.css"
}
```
`styles` is a **plugin-root-relative path that must live under `assets/`** (like
`screen`/`script`/`routes` are root-relative). It serves through the sandboxed
`/api/plugins//assets/...` route, so the file must be at
`/assets/plugin.css`. The injected `` is cache-busted with
`?v=`, so **bump your manifest `version`** whenever you rebuild the CSS,
or browsers may serve a stale copy within a session.
## 2. Build the stylesheet — utilities only, `preflight: false`
Core already ships Tailwind's base reset (preflight) once. Your plugin must
**not** re-apply it, or it would double the reset and fight core's styles. Build
with `corePlugins: { preflight: false }` so your sheet emits **only the utility
classes your files use**.
`tailwind.config.js` (in your plugin repo):
```js
/** Plugin stylesheet build — utilities only, scanned from this plugin's files.
* Regenerate assets/plugin.css with: bash build-tailwind.sh */
module.exports = {
corePlugins: { preflight: false }, // core owns the single base reset
content: [
'./screen.js',
'./settings.html',
'./screen.html',
// add any other file that carries Tailwind classes (e.g. './tour.json')
],
theme: {
extend: {
// Re-declare any core theme tokens you reference so they compile here.
colors: {
dark: { 900: '#050508', 800: '#0a0a12', 700: '#10101e', 600: '#181830', 500: '#1e1e3a' },
accent: { DEFAULT: '#4080e0', light: '#60a0ff', dark: '#2060b0' },
gold: '#e8c040',
},
fontFamily: { display: ['"Inter"', 'system-ui', 'sans-serif'] },
},
},
// Mirror only the dynamically-built classes your code generates at runtime
// (Tailwind can't see them textually). Drop this if you have none.
safelist: [
{ pattern: /^(bg|text|border)-(dark|accent)(-.+)?$/ },
],
plugins: [],
};
```
Input CSS — **`@tailwind utilities;` only** (no `@tailwind base`, that's the
preflight you're disabling):
`_plugin.src.css`:
```css
@tailwind utilities;
```
Build script `build-tailwind.sh` (run at your plugin's release time — the output
is committed; end users never build):
```bash
#!/usr/bin/env bash
set -euo pipefail
cd "$(dirname "$0")"
# Pin the same Tailwind 3.x core uses so output stays diff-stable.
exec npx -y tailwindcss@3.4.19 \
-c tailwind.config.js \
-i _plugin.src.css \
-o assets/plugin.css \
--minify
```
```bash
bash build-tailwind.sh # writes assets/plugin.css — commit it
```
## 3. Rules (inherited from the constitution)
- **No Play CDN, no runtime CSS JIT** — anywhere, ever. Same rule that binds core.
- **`preflight: false`** — utilities only; core ships the one base reset.
- **`styles` under `assets/`** — it serves through the sandboxed asset route;
`..`, absolute paths, and NUL bytes are rejected by `safe_join`.
- **Bump `version` on every CSS rebuild** so the `?v=` cache-buster fetches fresh.
- Plugins without `styles` are unaffected and inject no ``.
## How it works (for reference)
- The loader derives a manifest-only `has_styles` boolean and passes the `styles`
path through to `/api/plugins` — no plugin code is imported
(`plugins/__init__.py::_nav_entry`).
- The frontend (`static/app.js::_injectPluginStyles`) injects one
`` (the `styles` value —
e.g. `assets/plugin.css` — appended to `/api/plugins//`) into ``, **before** the
screen markup so styles are present on first paint. It's deduped by version: a
plugin upgrade swaps the old `` for the new one; re-activation never piles
up duplicates.
- The stylesheet is served by the existing
`/api/plugins//assets/` route as `text/css`.