Cascading Style Sheets (CSS) are a stylesheet language used to describe the presentation of a document written in HTML or XML (including XML dialects like SVG or XHTML). CSS describes how elements should be rendered on screen, on paper, in speech, or on other media.
CSS is one of the core languages of the open web and has a standardized W3C specification. Developed in levels, CSS1 is now obsolete, CSS2.1 is a recommendation, and CSS3, now split into smaller modules, is progressing on the standardization track.
- CSS Reference
An exhaustive reference for seasoned Web developers describing every property and concept of CSS.
- CSS Tutorials
Our CSS Learning Area contains a wealth of tutorials to take you from novice level to being comfortable with CSS, covering all the fundamentals.
- CSS Introduction
If you're new to web development, be sure to read our CSS Basics article to learn what CSS is and how to use it.
Our CSS Learning Area features multiple modules that teach CSS from the ground up — no previous knowledge required.
- Introduction to CSS
- This module gets you started with the basics of how CSS works, including selectors and properties, writing CSS rules, applying CSS to HTML, how to specify length, color, and other units in CSS, cascade and inheritance, box model basics, and debugging CSS.
- Styling text
- Here we look at text styling fundamentals, including setting font, boldness, and italics, line and letter spacing, and drop shadows and other text features. We round off the module by looking at applying custom fonts to your page, and styling lists and links.
- Styling boxes
- Next up, we look at styling boxes, one of the fundamental steps towards laying out a web page. In this module we recap the box model then look at controlling box layouts by setting padding, borders and margins, setting custom background colors, images and other features, and fancy features such drop shadows and filters on boxes.
- CSS layout
- At this point we've already looked at CSS fundamentals, how to style text, and how to style and manipulate the boxes that your content sits inside. Now it's time to look at how to place your boxes in the right place in relation to the viewport, and one another. We have covered the necessary prerequisites so can now dive deep into CSS layout, looking at different display settings, traditional layout methods involving float and positioning, and new fangled layout tools like flexbox.
- CSS Reference: An exhaustive reference for seasoned Web developers describing every property and concept of CSS.
- CSS key concepts:
Tools for CSS development
- The W3C CSS Validation Service checks if CSS is valid. This is an invaluable debugging tool.
- Firefox Developer Tools allow viewing and editing live CSS of a page via the Inspector and Style Editor tools.
- Firebug extension for Firefox, a popular extension of that navigator that allows to edit live CSS on watched sites. Very practical to test some changes, though this extension does much more.
- Web Developer extension for Firefox also allows to watch and edit live CSS on watched sites. Simpler than Firebug, though less powerful.
- Miscellaneous CSS tools.
- Firefox: bug 1323667