Although CSS was first introduced in the mid 1990s, it did not become a mainstream tool among web designers and masters until more recent years. This is unfortunate, because there are millions of poorly designed web sites cluttering the internet that could be easily improved with the help of CSS.
So what exactly is CSS? CSS is an acronym that stands for Cascading Style Sheets. The term Cascading Style Sheets implies two things. First off, the style sheets are cascading. This means that multiple style sheets can be used for a single web page. Additionally, the term “cascading” also refers to the way a style is determined in the event that more than one rule matches a single element. The second thing that is implied by the name Cascading Style Sheets is that the purpose of CSS is to style web pages. Whereas the purpose of HTML (or XHTML) is to define the structure of a web page, the purpose of CSS is to define the presentation.
The reason that so many web pages have broken layouts in different browsers is because they try to use HTML to control the structure and presentation of the page. The most common abuse of HTML is attempting to use tables as a presentation method. Although you may be able to achieve the look you want in a single browser, your web page will look broken and distorted in many other browsers. The only time that tables should be used is to hold a set of data (such as the results from a scientific experiment). If you do have a legitimate use for tables on your web page, you can even use CSS to style your table and make it more attractive.
By taking the time to learn CSS, you will be able to create a web page that looks much more consistent across a variety of browsers.