What Is a .css File? .css Format, MIME & How to Open

Quick facts

Extension.css

File typeCSS Stylesheet

MIME typetext/css

CategoryData & Text

CharsetUTF-8

CompressibleYes

Format familycss

What is .css

What is a .css file?

A .css file is a CSS Stylesheet — Cascading Style Sheets file describing web page presentation.

In the mime-db registry it maps to text/css with UTF-8 encoding, and it is marked as compressible. When serving .css over HTTP, set the Content-Type header as shown in Developer info below.

Related entities: it maps to text/css and is used by CSS among others — and is delivered over HTTP via the Content-Type header.

How to open .css files

Use VS Code or Chrome DevTools to open and edit .css files.
Any text editor (Notepad, VS Code) can inspect the raw content as text.

Developer info

When served over HTTP, responses should set the following header:

Content-Type: text/css; charset=utf-8

Common software that reads/writes .css:

VS CodeChrome DevTools

Relation chain

.cssextension of

format

cssserved as

mime type

text/csssent via header

http header

Related extensions

Related MIME types

Related programming languages

CSS

.css

Common uses

Configuration files
Data interchange between systems
API request and response payloads
Logs and data exports

How to edit .css files

Open the file with VS Code, make your changes and save.
Most editors preserve the original formatting and encoding — avoid changing the charset.

How to create .css files

Create a new file and save it with the .css extension, or export this format from VS Code.

Example

.card {
  padding: 1rem;
  border-radius: 8px;
  background: #fff;
}

Frequently asked questions

What programs can open .css files?

Common options include VS Code, Chrome DevTools. You can also open many of these files with built-in viewers or a browser.

How do I create a .css file?

Create a new file in any text editor or the app that owns the format and save it with the .css extension.

What is the relationship between .css and the text/css MIME type?

text/css is the media type identifier used for .css files during network transfer (for example in the HTTP Content-Type header).

Sources & standards

Updated 2026-09-13

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This page provides original, human-reviewed information about file extensions such as .css, the File Extension Reference and related concepts. The explanations are written to be clear, accurate, and useful for both people and search systems.

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