CSS Supported Positioning and Selection

Absolute Positioning

The content box - this one - uses absolute positioning. That has advantages and disadvantages. Using absolute positioning on an element removes it from the normal page flow. All the other elements ignore the positioned content and so may overwrite it or otherwise collide if your design doesn't manage those things.

However, it can be very useful to have some elements fixed and allow others to flow with the changing screen sizes and sizes of other adjacent elements.

This box has absolute positioning with top at 30px, left 200px, and width of 700px. This eliminates all text flowing within this box. As the browser window gets smaller the text is simply truncated.

Selection

The navigation bar, on the left, uses CSS to emphasize selection. As the mouse hovers over a link, the link is framed in a gray border, its background changes to white, and its padding increases. This creates some visual emphasis that may be useful for navigation, but can easily be overdone.