CDN — Vanilla HTML

The csszyx package ships a self-contained IIFE runtime that processes sz="..." attributes directly in vanilla HTML. Drop one <script> tag, write sz attributes the same way you would in JSX, and Tailwind classes appear at runtime.

This guide pairs with the VS Code Extension — same authoring experience (autocomplete, hover, syntax highlight) for sz= attributes in .html files.

Quick start

<!DOCTYPE html>
<html>
<head>
    <!-- 1. Tailwind v4 CDN — required (csszyx generates class names, Tailwind generates the CSS) -->
    <script src="https://unpkg.com/@tailwindcss/browser@4"></script>

    <!-- 2. csszyx runtime — pin to a specific version for production -->
    <script src="https://unpkg.com/csszyx@0.5.0"></script>

    <!-- 3. Anti-FOUC — hide elements until the runtime has compiled them -->
    <style>
        [sz]:not(.sz-ready) { visibility: hidden; }
        .sz-ready, .sz-ready [sz] { visibility: visible; }
    </style>
</head>
<body sz="{ p: 8, bg: 'slate-950', color: 'slate-200', minH: 'screen' }">
    <h1 sz="{ text: '4xl', fontWeight: 'bold', color: 'blue-500', mb: 4 }">
        Hello csszyx
    </h1>
    <p sz="{ text: 'lg', color: 'slate-400' }">
        No bundler. No JSX. Just attributes.
    </p>
</body>
</html>

Script order matters

The runtime walks the DOM, compiles each sz attribute into Tailwind class names, removes the sz attribute, then adds the resulting classes to the element’s class list. Tailwind v4’s JIT must see those classes after csszyx has written them, which is why the Tailwind script comes first in the <head>.

Order in `<head>`	Result
Tailwind → csszyx	✅ JIT picks up classes csszyx writes
csszyx → Tailwind	❌ JIT scans before classes exist; styles missing

Pinning versions

Always pin a specific version for production. CDN providers honor the unpkg and jsdelivr fields in package.json and serve the IIFE bundle directly at the package root URL:

<!-- unpkg -->
<script src="https://unpkg.com/csszyx@0.5.0"></script>

<!-- jsdelivr -->
<script src="https://cdn.jsdelivr.net/npm/csszyx@0.5.0"></script>

Avoid csszyx@latest in production — a major bump would silently break the page.

Anti-FOUC (recommended)

Without the anti-FOUC CSS, users see a flash of unstyled content while the runtime walks the DOM. The runtime adds sz-ready to <body> after the initial pass, so a single CSS rule eliminates the flash:

[sz]:not(.sz-ready) { visibility: hidden; }
.sz-ready, .sz-ready [sz] { visibility: visible; }

This is automatically injected by npx csszyx migrate public/ when converting an existing site — see Migrate.

Object syntax

Same as JSX sz={{ ... }}, but quoted as a single HTML attribute value. Use single quotes inside (HTML attribute is double-quoted):

<div sz="{ p: 4, bg: 'blue-500', hover: { bg: 'blue-600' } }">…</div>

Outer braces are optional — these are equivalent:

<div sz="{ p: 4, bg: 'red-500' }">…</div>
<div sz="p: 4, bg: 'red-500'">…</div>

The runtime auto-wraps when braces are missing, so the VS Code extension’s implicit syntax works out of the box.

Dynamically added elements

The runtime installs a MutationObserver on <body>, so any element added later (by frameworks, scripts, fragment swaps, htmx, Alpine.js, etc.) is processed automatically:

const card = document.createElement('div');
card.setAttribute('sz', "{ p: 4, bg: 'emerald-500', rounded: 'lg' }");
document.body.appendChild(card);
// → runtime sees it, compiles sz → class, removes sz attr

The observer recurses into subtrees, so inserting a parent with [sz] descendants processes them all in one dispatch.

Local dev (offline)

If you can’t depend on a public CDN, copy the bundle locally:

npm install csszyx@0.5.0
cp node_modules/csszyx/dist/browser.iife.js public/csszyx.js

Then reference the local file:

<script src="/csszyx.js"></script>

The IIFE is fully self-contained — no other csszyx files needed.

Limitations

No build-time mangling — class names are full Tailwind utilities (p-4, bg-blue-500, …), not the mangled z/y/x form. Mangling requires the build-time plugin pipeline, which doesn’t fit a CDN script.
Runtime evaluation is per-element — large pages with thousands of [sz] elements pay a per-element parse + transform cost on first load. For high-volume use, prefer the build-time plugin (csszyx/vite, csszyx/webpack).
Tailwind CDN is JIT-only — for production, ship a built Tailwind CSS file and serve it from your origin.

Demo

The repository ships a working demo at playground/vanilla-html/index.html covering object syntax, variants, dynamic elements, and the full anti-FOUC flow. Clone the repo and:

pnpm --filter @csszyx/playground-vanilla-html dev

Then open the URL the dev server prints.