Set up Master CSS in Svelte

Guide to setting up Master CSS in your Svelte project.

Master CSS Runtime Rendering observes changes in DOM class names at browser runtime, generates corresponding CSS rules, and injects them into the running style sheet.

Fixed style cost

All features work out of the box with ~16KB transfer cost

Fully automatic

Capture any program-generated class names

CSS lifecycle

CSS is generated on demand and frees memory when not in use

Quick start

Clone the example

Copy-paste the following commands to quickly start using the

You can skip all installation steps.

npx degit master-co/css/examples/svelte-with-runtime-rendering my-project
cd my-project
npm install @master/css.svelte@beta
npm install
npm run dev -- --open


Create a project

If you don't have a Svelte project, create one first. It's recommended to refer to Svelte Kit.

npm create svelte@latest project
cd project
npm install

Install Master CSS

Install Master CSS Svelte into your project via package managers.

npm install @master/css.svelte@beta

Initialize configuration file

Run npx mcss init to create a configuration file master.css.ts.

npx mcss init

Allow configuration file

Add ./master.css.ts to the server.fs.allow section in vite.config.ts to be allowed by the server file system.

Accessing files outside this directory list that aren't imported from an allowed file will result in a 403.

import { sveltekit } from '@sveltejs/kit/vite'
import { defineConfig } from 'vite'
export default defineConfig({
plugins: [sveltekit()],
server: {
fs: {
allow: ['./master.css.ts']

Set up CSS runtime engine

Register the <CSSProvider> in src/routes/+layout.svelte.

import { CSSProvider } from "@master/css.svelte";
import config from '../../master.css';
import Header from "./Header.svelte";
import "./styles.css";
<svelte:component this={CSSProvider} config={config}>
<slot />

Avoid flash of unstyled content

Add display: 'none' in <html> to avoid FOUC caused by the runtime engine not yet injecting CSS rules.

<!DOCTYPE html>
<html lang="en" style="display:none">

Launch server

Run npm run dev -- --open to start your Svelte development server

npm run dev -- --open

Start using Master CSS

Now style your first element using Master CSS syntax!

<h1 class="font:40 fg:blue font:heavy italic m:50 text:center">Hello World</h1>

Open your browser to watch the changes.


Hello World

MIT License © Aoyue Design LLC.