The pages in a Drupal site obtain their style-related information from associated style sheets, which are held in the site's theme. Using style sheets gives designers excellent, fine-grained control over the appearance of web pages, and even allows you to produce some great effects. The appearance of pretty much every aspect of the site can be controlled from within a theme, and all that is needed is a little knowledge of fonts, colors, and style sheet syntax.
Before we go any further, it will make life easier if you have a readymade list of the type of things you should look at setting using the style sheet. The following is a list of the most common areas (defined by HTML elements) where style sheets can be used to determine the look and feel of a site's:
Background
Text
Font
Color
Images
Border
Margin
Padding
List
As well as being able to change all these aspects of HTML, you can also apply different effects depending on whether certain conditions, like a mouse hovering over the specified area...