What do the sample stylesheets contain?

Custom properties, a body rule and a long list of class rules, with no @import rules or external URLs.

What is the MIME type of a CSS file?

The MIME type is text/css. The file extension is .css.

Is a sample CSS file the same as a dummy or example CSS file?

Yes. Sample, test, dummy and example CSS files are different names for the same thing: a CSS file with known contents that stands in for a real one. Any file on this page will do wherever a tutorial or a test plan asks for a dummy CSS file.

Free CSS sample files

Stylesheets that control how web pages look. Download valid CSS test files in 4 exact sizes, from 1 KB to 1 MB, each with a checksum.

Extension: .css
MIME type: text/css
Kind: Text
Category: Code

CSS files by size

Every file below is a valid Cascading Style Sheets file of exactly the stated size. Open a file's page for its checksum and contents, and to preview it in your browser before downloading.

CSS sample files by size
File	Size	Contents	Download
1 KB CSS samplesample-css-1kb.css	1 KB1,024 bytes	Features: Custom properties, class selectors, rem and px units	Download CSS
10 KB CSS samplesample-css-10kb.css	10 KB10,240 bytes	Features: Custom properties, class selectors, rem and px units	Download CSS
100 KB CSS samplesample-css-100kb.css	100 KB102,400 bytes	Features: Custom properties, class selectors, rem and px units	Download CSS
1 MB CSS samplesample-css-1mb.css	1 MB1,048,576 bytes	Features: Custom properties, class selectors, rem and px units	Download CSS

What is a CSS file?

CSS describes presentation: colours, spacing, layout and typography. A stylesheet is a list of rules, each pairing a selector, which chooses elements, with declarations that set properties.

Browsers ignore declarations they do not understand and carry on, which lets the language grow without breaking old pages.

How to recognise a CSS file

No signature bytes. CSS files are identified by parsing their content.

Extension	.css
MIME type	text/css
Standard	W3C CSS, published as modules
Encoding	UTF-8
Comments	/* */
Error handling	Invalid declarations are skipped

What to test for

These are the behaviours that most often go wrong when software handles CSS files.

With X-Content-Type-Options: nosniff, browsers refuse a stylesheet that is not served as text/css.

Strengths of CSS

Fault-tolerant: unknown rules are skipped rather than breaking the page.
Compresses and caches extremely well.

Limitations of CSS

The cascade makes large stylesheets hard to reason about.
A stylesheet in the document head blocks rendering until it loads.

Typical uses of CSS test files

Testing minifiers and bundlers
Checking asset pipelines and caching
Testing code editors and syntax highlighters

Software that opens CSS

All web browsers
PostCSS, Sass and Lightning CSS
Stylelint and editors

Specifications

W3C CSS snapshot

CSS sample files: questions

What do the sample stylesheets contain?: Custom properties, a body rule and a long list of class rules, with no @import rules or external URLs.
What is the MIME type of a CSS file?: The MIME type is text/css. The file extension is .css.
Is a sample CSS file the same as a dummy or example CSS file?: Yes. Sample, test, dummy and example CSS files are different names for the same thing: a CSS file with known contents that stands in for a real one. Any file on this page will do wherever a tutorial or a test plan asks for a dummy CSS file.