Welcome
CSS specifies a priority scheme to determine which style rules apply if more than one rule matches against a particular element. In this so-called cascade (hence Cascading Style Sheets), priorities or weights are calculated and assigned to rules, so that the results are predictable.
The CSS specifications are maintained by the World Wide Web Consortium (W3C) ➚.
Disadvantages of using "pure" CSS
Although CSS has some problems like e.g. margin-collapsing, float containment ..., one of the major disadvantages is the fact that browser support is inconsistent . Different browsers will render a CSS layout differently as a result of browser bugs or lack of support for CSS features. Notorious is Microsoft Internet Explorer, whose older versions, such as IE 6.0, implemented many CSS 2.0 properties in its own, incompatible way, misinterpreted a significant number of important properties, such as width, height, and float. Numerous so-called CSS "hacks" must be implemented to achieve consistent layout among the most popular or commonly used browsers. Pixel precise layouts can sometimes be, to say the least, hard to achieve across browsers.
I hope you'll find this site usefull. Along the way i'll provide tutorials and background stuff on CSS. However, this site is not intended to be a full intro. For more advanced CSS stuff, you can check out the links section.