CSS, short for Cascading Style Sheets is a style sheet language used for controlling how html is displayed on websites. Css document consist of set of rules where each rule represent a selector that matches elements inside a HTML document.
Take the following element inside a HTML document :
<a class="foo" href="https://codebeautify.net/">Code Beautify</a>
If we want to style the link e.g use red color and bigger font, we can map it thru the following css selector:
As you can see, we used the `a` tag as a selector element. This will cause also all links inside a document to have the same visual representation. Another way to map an HTML element inside a CSS document is by using the class name of the element as a CSS selector: