CSS

Class Selector

The selector in the example below targets an element by its class name. So every element with a class of "navigation" will receive the styles in question: /* matches HTML element with class="navigation" */ .navigation { width: 960px; margin: 0 auto; }

Universal Selector

The universal selector matches any element within the context in which it's placed in a selector. In the example below, the * character is the universal selector: /* the asterisk character is the universal selector */ .navigation ul * { width: 100px; float: left; } So, any element that appears as a child descendant of the unordered list element inside an element that has a class of "navigation" will receive the declared styles. Universal selectors are generally discouraged for performance reasons.

CSS Syntax

A CSS rule has two main parts: a selector, and one or more declarations: p {color:red;text-align:center;} p- selector color:red→ declaration where: color→ property red →value

Combinator

A combinator is the character in a selector that connects two selectors together. There are four types of combinators. These four combinators help create: - descendant selectors (with a space character), - child selectors (with the ">" character), - adjacent sibling selectors (with the "+" character), - general sibling selectors (with the "~" character). To dispel any confusion, here are those four combinators in use: /* In all 4 examples */ /* whatever appears between "div" and "p" is a combinator */ /* in the first example, the combinator is a space character */ div p { color: #222; } div>p { color: #333;} div+p { color: #444; } div~p { color: #555; }

Keyword

A keyword is a value for a property and is somewhat like a reserved word for a particular property. Different properties have different keywords, and all properties allow the keyword "inherit". In the example below, the value "auto" is a keyword. #container { height: auto; /* "auto" is a keyword */ } As an aside, I would argue that !important qualifies as a keyword, based on how keywords are differentiated from values.

Pseudo-Class

A pseudo-class works similarly to a regular CSS class, except it's not explicitly declared in the HTML. In the example below, the pseudo-class is added to the anchor element: /* the word "hover" along with the preceding colon is the pseudo-class */ a:hover { text-decoration: none; } A pseudo-class always has a single colon followed by a keyword of some sort, with no space before or after the colon. Other pseudo-classes include :visited, :focus, and :first-child.

Inline Styles

An inline style loses many of the advantages of style sheets by mixing content with presentation. Use this method sparingly! To use inline styles you use the style attribute in the relevant tag. The style attribute can contain any CSS property. The example shows how to change the color and the left margin of a paragraph: <p style="color:sienna;margin-left:20px">This is a paragraph.</p>

id Selector

The id selector is used to specify a style for a single, unique element. The id selector uses the id attribute of the HTML element, and is defined with a "#". The style rule below will be applied to the element with id="para1": #para1 {text-align:center;color:red;}

ID Selector

The selector in the example below targets an element by its ID. So every element with an ID of "navigation" will receive the styles in question: /* matches HTML element with id="navigation" */ #navigation { width: 960px; margin: 0 auto; } In HTML, a page will have validation errors if two or more elements share the same ID.

Comment

A comment has no effect on the display of the page that's styled; it's for the CSS author to read and better understand the code. Comments are universal to (as far as I know) all programming and related languages. In the example below, the line that says "this is for IE6″ is a comment: /* this is for IE6 */ * html #box { width: 200px; }

Declaration Block

A declaration block is the section of CSS where the property/value pairs appear. In the example below, everything found between the curly braces (not including the comments) is a declaration block: body { font-family: Arial, sans-serif; /* starts with this line */ color: #555; font-size: 14px; line-height: 20px; /* ends here, before the closing curly brace */ }

Declaration

A declaration is generally any single line of CSS that appears between the curly braces, whether shorthand or longhand. In the example below, everything after the first curly brace, and before the last curly brace (not including the comment) is a declaration: body { font-family: Arial, sans-serif; /* this line is a declaration */ } In this next example, there are two declarations between the curly braces: body { font-family: Arial, sans-serif; /* one declaration */ color: #555; /* another declaration */ }

Property

A property is what appears before the colon in any line of CSS. In the example below, the word "width" is the property. #box { width: 200px; /* the property is "width" (without the colon) */ }

Pseudo-Element

A pseudo-element is not the same as a pseudo-class. While a pseudo-class matches elements that actually exist, pseudo-elements target "virtual" elements that can change depending on the actual HTML. CSS2 pseudo-elements use a single colon and CSS3 pseudo-elements use a double colon. In the example below, the first rule set uses a CSS2 pseudo-element, and the second rule set uses a CSS3 pseudo-element: /* "first-letter" including the preceding colon is the pseudo-element */ p:first-letter { display: block; float: left; margin: 0 5px 5px 0; } /* CSS3 pseudo-elements have double colons */ ::selection { background: green; }

Rule Set

A rule set is a single section of CSS including the selector, the curly braces, and the different lines with properties and values. The code in the example below comprises one rule set: /* the rule set starts with the line below */ body { font-family: Arial, sans-serif; color: #555; font-size: 14px; } /* ends with the closing curly brace above */

Selector

A selector is the part of the CSS line that selects what element to target with the property/value pair. In the example below "#container #box" is the selector: /* the selector is everything on the first line */ /* excluding the opening curly brace */ #container #box { width: 200px; }

Statement

A statement in CSS is any at-rule or rule set. In the example below, there are two statements; one is an at-rule, and the other is a rule set: /* the at-rule below is a statement */ @import url(secondary.css); /* the entire rule-set below is a statement */ body { font-family: Arial, sans-serif; color: #555; font-size: 14px; }

Value

A value is what appears immediately after the colon in any line of CSS. In the example below, the "200px" is the value. #box { width: 200px; /* after the colon, without the semi-colon */ } If you use shorthand, a single declaration could have multiple values.

At-Rule

An at-rule has nothing to do with Star Wars. An at-rule is an instruction given in a CSS document using the @ character. An at-rule could have a declaration block or a simple string of text. The example below has two different at-rules: @import url(secondary.css); @media print { #container { width: 500px; } } The at-rule is not just the "@media" or "@import" part at the beginning; the entire instruction comprises the complete at-rule.

Attribute Selector

An attribute selector selects an element to style based on an attribute and/or attribute value. The example below targets certain paragraph elements based on the existence of a "style" attribute: /* matches elements with style="[anything]" */ p[style] { color: #1e1e1e; } The example below targets certain input elements based on the existence of a type attribute with a value of "text": /* matches input elements with type="text" */ input[type="text"] { border: solid 1px #ccc; } In each example above, everything before the first curly brace is an attribute selector.

Element Type Selector

An element type selector is a selector that targets an element by the tag name. The selector in the example below is an element type selector, because it doesn't use a class, ID, or other selector to apply the given styles. Instead, it directly targets all HTML5 <nav> elements: /* matches an HTML element by name */ nav { font-family: Arial, sans-serif; color: #555; font-size: 14px; }

External Style Sheet

An external style sheet is ideal when the style is applied to many pages. With an external style sheet, you can change the look of an entire Web site by changing one file. Each page must link to the style sheet using the <link> tag. The <link> tag goes inside the head section: <head> <link rel="stylesheet" type="text/css" href="mystyle.css"> </head>

Identifier

An identifier can be anything that appears as a property, id, class, keyword value, and at-rule. In the example, below there are four identifiers: /* "body", "background", "none", and "font-size" are identifiers */ body { background: none; font-size: 14px; } /* "14px" is not an identifier */ The word "body" is an identifier; the word "background" is an identifier; the word "none" is an identifier; and the word "font-size" is an identifier. The last value "14px" is not an identifier, because it's not a keyword

Internal Style Sheet

An internal style sheet should be used when a single document has a unique style. You define internal styles in the head section of an HTML page, by using the <style> tag, like this: <head> <style> hr {color:sienna;} p {margin-left:20px;} body {background-image:url("images/back40.gif");} </style> </head>

Cascading order

Generally speaking we can say that all the styles will "cascade" into a new "virtual" style sheet by the following rules, where number 1 has the highest priority: 1. Inline style (inside an HTML element) 2. Internal style sheet (in the head section) 3. External style sheet 4. Browser default Note: If the link to the external style sheet is placed after the internal style sheet in HTML <head>, the external style sheet will override the internal style sheet!