The Parts of a CSS Rule All rules, regardless of their locations or types, have the following structural elements: n Selectors are the alphanumeric characters that identify a rule. A selector can be an HTML tag selector, a class selector, an ID selector, a universal selector or a combination of those basic selectors to create context based styles. Properties identify what is being defined. Several dozen properties are available; each is responsible for an aspect of the page content’s behavior and appearance. Values are assigned to a property to define its nature.

CSS and HTML When HTML was first created, style properties were defined directly in the code. However, rather than just adding more and more tags to HTML, the W3C introduced Cascading Style Sheets to fill the design void in straight HTML, allowing the Web to become semantic in structure. For example. In HTML, the strong tag does one thing and one thing only: It makes text “stronger,” usually by making it bolder. However, using CSS, you can “redefine” the tag so that it not only makes text bolder, but also displays text in all caps and in a particular font to add more emphasis.

This is a visual guide to show each region's placement on the page.

Hex or Decimal? Until recently, it was assumed that colors should always be declared in RGB hexadecimal notation. In fact, I still meet designers and developers who are completely unaware that they have alternatives. RGB decimal has been around for quite awhile and will work in any browser you want to throw it at. But which is “better”? I personally find that it’s much easier to envision a color in decimal numbers (which I’ve used all my life) than in hex values. I can look at the value 135, 127, 107 and know it’s a reddish beige much faster than if I see 877f6b.