Elements can be classified according to the way they’re displayed—inline or block. By default, every tag has a display style that defines how it will fit with the surrounding tags. You can use the display property to define whether an element includes line breaks above and below (block), is included with other elements without hard line breaks (inline), is treated as part of a list (list), or is displayed at all (none).  To set an element’s display type:
1. Start your declaration by typing the display property name in the CSS declaration block, followed by a colon (:) display:

It’s sometimes difficult to keep track of all the values that you are using in your design. It’s unlikely that CSS will ever include constants, so it will help to keep notes in an easy-to-reference location in your document. Creating a glossary of colors and types leads to more consistent and attractive designs  Although section headers and dividers really aren’t anything more than CSS comments, they do help organize your CSS and allow you to quickly scan your code to locate particular CSS rule groups. If you have established a TOC, I recommend reflecting that organization here.

browser CSS extensions In addition to supporting the specified CSS properties set by the W3C, a browser developer will occasionally introduce browser-specific properties. This is often done for one of two reasons: n A spec is still under development by the W3C but the browser developer wants to start using the style now. The browser developer wants to try a new idea but doesn't want to wait for the W3C to accept it and begin work on it, which can take years.