Dynamic HTML (DHTML) describes a set of new technologies for designing Web pages that allow new and more precise formatting features, along with faster access for users.
DHTML is not a new language. DHTML is simply a snazzy name for a set of new features that recent Web browsers are equipped to interpret and use. DHTML features work only within the context of a standard HTML document.
DHTML uses two new pieces in concert with HTML. The first is scripts that run on the user's browser, written in a scripting language such as JavaScript or VBScript. The other is Cascading Style Sheets, a new method of specifying exact styles for a Web page's elements.
DHTML allows you to specify many details of the way you want text to display in a user's browser, including font size, color, and background. You can also precisely position text blocks and other elements in a Web page without using tables. One of DHTML's most impressive features, however, is its ability to instantly change the appearance and content of the cu rrent Web page in response to user actions. While this feature may sound similar to options already available in HTML, such as links and pop-up boxes, dynamic HTML makes changes instantly without contacting the Web server, and allows you almost unlimited formatting options, which plain HTML can't do.
DHTML features require familiarity with two main technologies. To manipulate Web page styles dynamically, you need to learn the structure and syntax of cascading style sheets (CSS). Additionally, in order to make your Web pages interactive with user actions, you need to become familiar with a simple scripting language. I recommend learning JavaScript, as it's the only scripting language compatible with both Navigator and Internet Explorer.
Cascading Style Sheets (CSS) is the term for a method of specifying detailed display information for your Web pages. "Style sheets" refers to the insertion of style details for individual text blocks, certain tags through the Web page, or even for tags among several Web pages. "Cascading" describes the hierarchical structure this formatting follows, allowing you to make changes to style specifications at lower levels (such as a specific line) while higher-level formatting (for the tag or section) remains in force.