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What is CSS? CSS (cascading stylesheets) is a simple mechanism for controlling the style of a Web document without compromising its structure. By separating visual design elements (fonts, colors, margins, and so on) from the structural logic of a Web page, CSS give Web designers the control they crave without sacrificing the integrity of the data thus maintaining its usability in multiple environments. In addition, defining typographic design and page layout from within a single, distinct block of code without having to resort to image maps, tags, tables, and spacer GIFs allows for faster downloads, streamlined site maintenance, and instantaneous global control of design attributes across multiple pages. How CSS Works CSS overrides the browsers default settings for interpreting how tags should be displayed, letting you use any HTML element indicated by an opening and closing tag (including the tag) to apply style attributes defined either locally or in a stylesheet. Stylesheets contain rules, composed of selectors and declarations that define how styles will be applied.
The selector (a redefined HTML element, class name, or ID name) is the link between the HTML document and the style. There are two different kinds of selectors: types (HTML element tags) and attributes (such as class and ID names). A CSS declaration has two parts, a property (color) and a value (red). The basic syntax of a rule selector {property 1: value 1; property 2: value: An example (containing two declarations, as above) P {font-size: 8 pt; color: red} Local, Global, and Linked Stylesheets Local (inline) stylesheet declarations, specific to a single instance on a page, can be used instead of tags to specify font size, color, and typeface and to define margins, leading, etc. This is a local stylesheet declaration.
Global (embedded) stylesheet declarations, applicable to an entire document, are defined within the and tags, which precede the tag in the HTML document and are usually placed in the header. To embed a global stylesheet in your HTML document: Title [DOCUMENT BODY GOES HERE] Linked stylesheet declarations use a single stylesheet (in a separate file, saved with the. css suffix) to define multiple pages. A typical.
css file is a text file containing style rules, as here: P {font-family: non-serif; font-size: medium; color: red} H 1 {font-family: serif; font-size: x-large; color: green} H 2 {font-family: serif; font-size: large; color: blue} To apply a. css stylesheet (style. css in the example below) to an HTML page, a tag is added to the page header: Inheritance In cases where local, global, and linked style definitions conflict, the most specific stylesheet will generally take precedence: local overrides global, global overrides linked. Similarly, inline style attributes override ID, ID overrides class, and class overrides stylesheet-defined HTML elements. Units of Measure Throughout this CSS reference guide, abstract values (notably values involving units of measure) appear between angle brackets: .
They should be replaced by actual values as indicated in the key below. Length Units indicates a number followed by a unit of measure: 24 px. The number can be an integer or a decimal fraction, and can be preceded by + or -. Units can be absolute or relative: Absolute: mm, cm, in, pt, pc (millimeters, centimeters, inches, points, pica's) Relative: em, ex, px (the elements font height, the elements x-height, pixels) Font size may be defined in points, pixels, inches, or centimeters (pt, px, in, cm) or as a percentage. can be: xx-small, x-small, small, medium, large, x-large, xx-large.
can be: larger, smaller. Percentage Units indicates a number followed by a % sign: 50 %. In the text-indent, margin, padding, and width properties, percentage values are relative to the width of the parent element. In the font-size property, percentage values are relative to the font size of the parent element. In values, percentages can be used to express RGB values. Color Units can represent either or values, as defined below: can be: aqua, black, blue, fuchsia, gray, green, lime, maroon, navy, olive, purple, red, silver, teal, white, yellow can be: # rgb (rgb (, , ) represents a hexadecimal value, a decimal value, and a percentage.
CSS-P (Position) CSS-P allows you to explicitly determine the position of HTML elements, providing powerful layout control both for static documents and for dynamic, animated HTML-based content. There are two basic methods of positioning HTML elements using the position property. Absolute position lets you set an elements position arbitrarily that is, relative to its parent container and independent of the documents flow. Relative position allows an element to be offset relative to its natural position in the documents flow.
Position is specified with the top and / or left properties using a value (relative or absolute as appropriate). The visibility property sets the display state of the element, but doesnt affect its position in the layout: An element takes up the same space whether hidden or visible. Z-index is used to specify the stacking order of the positional elements above or below other HTML elements. The number value may be positive or negative, and must be an integer. Default z-ordering of elements in a document is back-to-front in the order of their appearance in the HTML. The overflow element is used to control the display of an elements contents in cases where they exceed its given dimensions.
It applies only to elements with the position property of type absolute. Dynamic aspects of managing positioned elements, like hiding, displaying, and movement, are implemented using an external scripting language, such as JavaScript. The top and left properties may be expressed as percentages. For other CSS-P properties listed, percentages do not apply. Attributes Class and ID Classes let you create grouping schemes among styled HTML tags by adding the style definition of a particular class to the style definitions of several different tags. In the stylesheet, a class name is preceded by a period (. ) to identify it as such: .
foo {property 1: value 1; property 2: value 2 } A very simple example: P {font-family: sans-serif; font-size: 10 pt} H 1 {font-family: serif; font-size: 30 pt} H 2 {font-family: serif; font-size: 24 pt}. red {color: red}. green {color: green}. blue {color: blue} The tags and classes can then be used in combination: This is rendered as 30 -point red serif text. This is rendered as 10 -point red sans-serif text. Or not: This is rendered as 10 -point sans-serif text in the default color.
The ID attribute is used for a uniquely defined style within a stylesheet. In the stylesheet, an ID name is preceded by a hash mark (#) to identify it as such: #foo {property 1: value 1; property 2: value 2 } Text rendered in the foo style. Text-Level Attributes: and The tag is generally used to apply a style to inline text: This text is rendered as foo-style and this is not. The tag is generally used to apply a style to a block of text, which can also include other HTML elements: The foo style will be applied to this text, and to this text as well. The style attribute provides a way to define a style for a single instance of an element: This text is rendered as red, 10 -point type The class, ID, and style attributed can be applied within the and elements. Used with class or ID, the and tags work like customized HTML tags, letting you define logical containers and apply a style to their contents.
Conclusion In conclusion CSS is a dynamic, innovative approach to creating web sites. Css freedom and reliability of code allows for pages to be created by the most novice web program and also allows for creativity of the more advanced users. CSS is the wave of the future in web programing, soon all sites will have a stylesheet controlling the style and form. Bibliography web Draft of the Cascading Stylesheets proposal web FORM-best CSS stylesheet editor. web The ISO/IEC JTC 1 /SC 18 /WG 8 Web Service look on this page for links to information about DSSSL and DSSSL-Lite (another proposed web-stylesheet language). Other DSSSL information can be found at: web The draft DSSSL standard.
web Suggestions on how to use the underlying SGML tag structure of the draft standard for searching, ftp. netcom. com / pub /no / novlepub /dsssl / dsssl -dt The draft standard in Dyna Text format. You need the files dsssl 96. zip, down 23. zip, readme.
txt and unzip. exe. You cannot use pk unzip. ftp. netcom. com / pub /no / novlepub /dsssl / src The SGML source files for the Dyna Web draft. 334
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