CSS

CSS is the style-sheet language used to describe the presentation of HTML documents — controlling layout, colors, fonts, spacing, and responsive behavior. First standardized by the W3C in 1996, it has evolved through multiple specification levels and now includes powerful features such as CSS Grid, Flexbox, custom properties (variables), and native animations. CSS files are plain text and are loaded alongside HTML; they have no standalone content but are essential to the visual rendering of virtually every website.

File extensions	.css
MIME type	text/css
Developer	W3C
First released	1996
Category	Other
Open standard	Yes

What opens CSS files

• Any text editor
• Visual Studio Code
• WebStorm
• All modern web browsers (rendered, not opened directly)

Browse File Formats

Reference details for 53 file formats — extensions, MIME types, what opens each one, and how they convert.

7Z Archives ABW Documents AI Images AVIF Images AZW3 E-books BMP Images CSS Other CSV Spreadsheets DjVu E-books DOC Documents DOCX Documents EPS Images EPUB E-books FB2 E-books GIF Images GZ Archives HEIC Images HTML Documents ICO Images ISO Archives JPG Images JSON Other Keynote Presentations Markdown Documents MOBI E-books Numbers Spreadsheets ODP Presentations ODS Spreadsheets ODT Documents OTF Other Pages Documents PDF Documents PNG Images PPT Presentations PPTX Presentations PSD Images RAR Archives RAW Images RTF Documents SVG Images TAR Archives TeX / LaTeX Documents TIFF Images TSV Spreadsheets TTF Other TXT Documents WebP Images WOFF / WOFF2 Other WPD Documents XLS Spreadsheets XLSX Spreadsheets XML Documents ZIP Archives