Cascading Style Sheets (CSS) is a language that describes how HTML should be rendered by the web browser. CSS level 3, or more simply CSS3, is the third major revision of the CSS standard. CSS is maintained by the CSS Working Group (CSSWG), a collection of interested individuals and companies, but guided by the W3C.

Because most browsers have built-in standards for how HTML tags should be rendered, such as how <h1> appears in a large bold font, you can override these built-in definitions with your own CSS rules. Your CSS code is stored parallel to your HTML code, and it is possible to share one CSS file with multiple HTML files. This simplifies making cosmetic changes to an entire website as all stylization is sourced from a ...

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