The biggest obstacle to the use of dynamic HTML is that, since many users are still using older browsers, a Web site must create two versions of each site and serve the pages appropriate to each user's browser version. This heading or any other element on the page can be changed as the result of a specified event such a mouse passing over or being clicked or a time elapsing. Thus, variations can be thought of as different properties of the object. Not only can element variations change text wording or color, but everything contained within a heading object can be replaced with new content that includes different or additional HTML as well as different text. For Web pages, a style sheet also describes the default background color or image, hypertext link colors, and possibly the content of page.
Style sheets help ensure consistency across all or a group of pages in a document or a Web site.
As the result of user interaction, a new style sheet can be made applicable and result in a change of appearance of the Web page. You can have multiple layers of style sheet within a page, a style sheet within a style sheet within a style sheet. A new style sheet may only vary one element from the style sheet above it. Layers can be programmed to appear as part of a timed presentation or as the result of user interaction. In Internet Explorer 4.0, Microsoft implements layers through style sheets.