Comandos Del Css

Cascading Style Sheets
Introduction
HTML allows designers to determine how a document is viewed in a browser over the World Wide Web (WWW) by applying tags that manipulate the appearance or assign styles to the text. The purpose of cascading style sheets (CSS) is to allow Web authors to manipulate a Web page's appearance without affecting its HTML structure (Rotter, Kahn, & Anderson; 2000). Forexample, if all sub-headings in a document need to be displayed in a larger font and italicized, then the appropriate HTML tags must be placed around each sub-heading in the text of the code. CSS allow designers to make these specifications without applying individual line code in the HTML document. Thus, CSS separate presentation and content on the Web (Nielsen, 1997). To facilitate theformatting of Web pages, the World Wide Web Consortium (W3C) developed guidelines for CSS. W3C has developed guidelines for two kinds of CSS, Level 1 and Level 2. Level 1, allow authors to define about fifty properties including fonts, color and background, text spacing, alignment, margins, box properties, and classification properties. Level 2, extends these property definitions by 70. The additionaldefinitions beyond screen-based presentation and include media-specific presentations, such as visual browsers, aural devices, printers, Braille devices, and handheld devices. Level 2, also supports content positioning, downloadable fonts, table layout, features for internationalization, automatic counters and numbering, and some properties related to user interface (Nielson, 1997).

Significanceof CSS
If properly applied, CSS can give a designer the ability to separate content and presentation. However, not all Web designers are convinced that CSS are reliable tools or that content and format should be separated at all in Web publishing. Advocates of CSS claim that CSS allow for cleaner HTML, which is easier in development stages and facilitates in the creation of templates (Young,1997). Additionally, page-wide or sitewide changes are much easier to implement when using CSS (Rotter, Kahn, & Anderson; 2000). Supporters of CSS also recognize limitations, one of which is Web browser support. Versions 3.0 of Opera and Microsoft Internet Explorer and Version 4.0 of Netscape Navigator support properties for Level 1, and 4.0 and later versions of all three browsers support propertiesfor Level 2. Some Web development tools have solved the problem of

browser support by translating style sheet properties into HTML code, but Dreamweaver is one of the only programs that will automatically convert styles to HTML tags. In addition to the limitations of browser support, other concerns about designers using CSS to override an individual’s browser settings have been raised. Whendesigners misuse style sheets, pages become inaccessible. (Pozadzides & Quinn, 1997) Some Web authors oppose the use of CSS. For example, Korpela claims that CSS are not sophisticated enough to solve the serious problems involved in separating format and content on the Web. The complexity of CSS invites misunderstandings and misuses. In addition to flaws in the basic setup and structure, Korpelaargues that the fundamental principal behind the development of CSS is archaic because CSS tries to fit publishing on the Web into the traditional publishing model, where format and content are separate issues. In Web publishing, where there are many technological implications of formatting, it is imperative for formatters to understand the constraints of the Web and to understand mark up languages.Therefore, he believes that we should not try to separate the two functions. Korpela’s argument against creating tools to facilitate Web development with an archaic mind set and an “in the box” approach is valid. CSS are not perfect. CSS can, however, help designers to set certain styles more accurately and mre conveniently, and this point has caused many Web designers to think highly of CSS....