Live CSS preview
Every rule you write re-renders instantly — see colors, spacing and layout change as you type.
Free CSS playground
CSS online compiler — write CSS, see it live
FastCompiler's CSS online compiler gives you a live editor for layouts, colors, typography, flexbox and grid. Every keystroke updates the preview instantly — no sign-up, no download.
What is a CSS compiler? A CSS compiler online (also called a CSS playground) takes the styles you write and applies them to real markup instantly, so every rule, color and layout change renders live — no build tools, no preprocessors, no setup. With the FastCompiler CSS compiler online, you edit the style.css tab and the preview updates as you type, making it a true online CSS editor for flexbox, grid, typography and animations. It is Free, with No Sign-Up and 100% Offline support after load, and everything auto-saves privately in your browser. Students grasp the cascade faster, and designers test responsive ideas in seconds.
Why use this CSS compiler?
Flexbox & grid sandbox
The starter code includes a flexbox layout; swap to grid and play with grid-template-columns freely.
Private by default
Your styles never leave your device. Everything compiles locally, offline.
Auto-save
Work is saved to your browser's local storage automatically, so experiments survive a refresh.
Export any time
Copy the combined HTML and CSS or download a single file to keep experimenting elsewhere.
Full-page preview
Open the styled result in a new tab to check it at real browser width.
How to run CSS online in 3 steps
Running CSS online with FastCompiler takes three steps — and the playground above is already loaded.
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1
Write or paste your CSS
Edit the style.css tab — or paste a full stylesheet. Switch to the index.html tab if you want custom markup underneath.
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2
Watch it compile live
The preview re-renders automatically as you type, so flexbox, grid and colors update instantly with no refresh.
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3
Export or share
Copy the combined source, open the styled page in a new tab, or download it as a single HTML file.
What to try in the playground
Build a card layout
Use flexbox to line up three cards, then add hover transforms and box-shadows to make them lift.
Center anything
Try display: grid; place-items: center on the body — the classic two-line centering trick.
Design a button
Play with gradients, border-radius and transitions to craft a pill button worth copying into a project.
Copy-paste examples
3 CSS examples to try right now
Paste each block into the style.css tab above — the preview updates live. By Juwel, last updated September 8, 2026.
1. Two-line centering (grid)
* { box-sizing: border-box; }
body { display: grid; place-items: center; min-height: 60vh; margin: 0; }
.card { padding: 24px 32px; border-radius: 12px; box-shadow: 0 8px 24px rgba(0,0,0,.12); }2. Flexbox cards that wrap
.row { display: flex; gap: 16px; flex-wrap: wrap; }
.row > * { flex: 1 1 180px; padding: 20px; background: #f8fafc; border: 1px solid #e2e8f0; border-radius: 10px; }3. Pill button with transition
.btn { background: linear-gradient(135deg, #4f46e5, #7c3aed); color: #fff; padding: 10px 22px; border-radius: 999px; transition: transform .15s ease, box-shadow .15s ease; }
.btn:hover { transform: translateY(-1px); box-shadow: 0 6px 16px rgba(79,70,229,.35); }New here? Read how to run HTML, CSS & JavaScript online — then browse all FastCompiler tools.
Limitations & how it compares
This playground compiles vanilla CSS in your browser — no Sass/Less build step, no autoprefixer. Use it to learn the cascade, specificity and layout truthfully: what you see is your browser engine. For pre-processors, compile locally then paste the output here to preview.
vs CodePen/JSFiddle: CodePen and JSFiddle add vendor UI and cloud saves. FastCompiler is offline, private (localStorage only) and exports a single self-contained HTML file. Pair it with the CSS properties reference and HTML runner for full pages.
Reviewed by Juwel, founder & editor — tested on Chrome, Firefox, Safari and Android Chrome.
Frequently asked questions
How can I compile and test CSS online for free?
Use the FastCompiler CSS compiler above. Edit the style.css tab and the preview updates live — no software to install and no account needed.
Can I practice flexbox and grid in a CSS playground?
Yes. The starter code includes a flexbox layout you can rebuild, and you can switch the display property to grid and experiment with grid-template-columns and grid-template-areas.
Does the CSS compiler need an internet connection?
The compiler runs entirely in your browser. After the page loads once, your CSS work continues offline and auto-saves to local storage.
Can I use my own HTML with the CSS editor?
Yes. Switch to the HTML tab to edit the markup your styles apply to — or paste an entire page and style it from scratch.
How do I run CSS online with HTML?
Paste your markup in the index.html tab, write styles in style.css, and the preview renders both together instantly — no setup, download, or account.
What is the difference between a CSS compiler and a CSS playground?
They are the same thing here. Compiler emphasizes rendering your code live; playground emphasizes experimenting freely. Edit, break things, and iterate — your work auto-saves offline.
Is this online CSS editor free?
Yes. The CSS editor online is free forever with no sign-up. You get live preview, flexbox and grid sandbox, offline mode, and one-click download.