.css

Low risk

Cascading Style Sheets

The styling language for the web. Paired with HTML it controls colour, layout, animations, and media queries.

MIME types

text/css

Category

web

What opens this file

VS Code
Sublime Text
Browser DevTools

How to open by OS

Windows

VS Code, Sublime Text, browser DevTools.

Mac

VS Code, Sublime Text.

Linux

VS Code, Vim.

Ios

Working Copy, Play for Mac.

Android

Acode, Trebedit.

Safety notes

CSS itself cannot execute code, but @import and url() can fetch resources — enough to leak information if applied to untrusted input.

Common mistakes

Using modern selectors like :has() or position: sticky without checking support can break older browsers.
Global * transitions animate every element and tank performance on complex pages.

Related extensions

References

W3C CSS Specifications