This is the CSS Reference on Brugbart, use this in combination with the HTML and CSS Tutorials.
CSS is used by web-designers to change the appearance of HTML pages.
You can edit CSS using just about any normal text-editor. It is generally not recommended to use WYSIWYG tools, unless you fully understand the code, and are able to tell if the WYSIWYG editor has done things correctly.
If you are on the look-out for a free editor to use, be sure to check out: Web Designers Tools List