Using Cascading Style Sheets Module B: CSS Structure

Goals Understand how contextual, class and ID selectors work Understand how <div> and <span> work Understand how to build an external style sheet Understand how to create color, text and alignment styles

CSS Structure You now understand the basics of working with CSS You will now learn how to structure the CSS used by your documents

Internal Style Sheets You use an internal style sheet to create styles that apply to an entire document You create an internal style sheet within a <style> element placed within the document head The <style> element must include a type attribute, which is assigned a value of “text/css”

Internal Style Sheets Within the <style> element you create any style instructions for a specific element that are applied to all instances of that element contained in the body of the document The element to which specific style rules in a style sheet apply is called a selector

Internal Style Sheets

Contextual Selectors A contextual selector allows you to specify formatting for an element, but only when it is contained within another element You create a contextual selector by including two or more selectors in a declaration within a <style> element separated by spaces

Class Selectors Another method of applying styles is to use class selectors, which allow you to create different groups of styles for the same element You create a class selector within a <style> element by appending a name for the class to a selector with a period

Class Selectors You then assign the class name to the standard class attribute of elements in the document that you want to format with the class’s style definitions

ID Selectors An ID selector is similar to an inline style in that it allows you to create style declarations that are only applied to a single element in the document As with inline styles, you use an ID selector when you want to change the style of a single element on your Web page

ID Selectors The benefit to using ID selectors over inline styles is that they allow you to maintain all of your style declarations in a single location within the <style> element, as opposed to inline style declarations, which you must create within each element

External Style Sheets External style sheets are separate text documents containing style declarations that are used by multiple documents on a Web site You should create an external style sheet whenever you need to use the same styles on multiple Web pages on the same site

External Style Sheets You create an external style sheet in a text editor, the same as when you create XHTML documents However, you should save the document with an extension of .css

External Style Sheets The most popular way of accessing the styles in an external style sheet is to use the empty <link> element to link a document to a style sheet You place the <link> element in the document head

External Style Sheets You include three attributes in the <link> element: The href attribute that is assigned the Uniform Resource Locator (URL) of the style sheet The rel attribute that is assigned a value of “stylesheet” to specify that the referenced file is a style sheet The type attribute, which is assigned the same “text/css” value as the type attribute used in the <style> element

The <div> and <span> Elements The <div> element formats a group of block-level and inline elements with styles, whereas the <span> element formats a group of inline elements The only difference between these two elements is that the <div> element can contain block-level elements and also adds a line break after its closing tag

Cascading Order CSS uses an order of precedence to determine which styles to apply when a selector is formatted in different sources The least important style formatting is the browser’s default style settings

Cascading Order The cascading order of precedence for styles, starting with the least important to the most important, is as follows: Browser default External style sheets Internal style sheets Inline styles

Setting Color and Background Properties The color property sets the text color of an element Background properties set the background color or image that appears behind an element

Foreground and Background Color The color you apply with the color element is referred to as the foreground color Another type of color you can add to elements is background color, which you create with the background-color property

Foreground and Background Color The foreground color that is applied to an element’s text appears on top of an element’s background color

Foreground and Background Color The W3C strongly recommends that whenever you use the color property, you also include the background-color property to ensure that the foreground color text is placed on a suitable background In order to set background properties for the Web page itself, you declare them for the <body> element

Background Images To set an image to appear as the document background, you use the background-image property and assign to it a URL using the format url (url)

Background Images

The background Shorthand Property Several of the property categories include a special property called a shorthand property that allows you to set all of the properties in a category using one declaration

The background Shorthand Property The shorthand property for the background properties category is the background property Many of the properties for each category have unique values that are assigned to them

The background Shorthand Property The background-attachment property can be assigned the values “scroll” or “fixed”; neither of these values can be assigned to any other background property

Setting Text Properties You use text properties to specify the placement and appearance of text The difference between text properties and font properties is that text properties do not change the appearance of an element’s font Text properties adjust visual aspects such as word and letter spacing, text alignment, indentation, and so on

CSS1 Text Properties

Word and Letter Spacing Word spacing refers to the amount of space between words, whereas letter spacing refers to the amount of space between letters You set word spacing with the word-spacing property and letter spacing with the letter-spacing property

Text Decorations The text-decoration property modifies the appearance of text by adding the following “decorations” to the text: none, underline, overline, line-through, and blink

Text Decorations An underline value underlines the text, an overline value places a line over the text, and a line-through value places a line through the text, the same as the <del> element

Text Decorations One of the more common uses of the text-decoration property is to turn off the underline that appears beneath links for design purposes

Line Height By default, the line height in a document is set to single-space You use the line-height property to change the default line of an element from single-spacing to something else

Line Height The line-height property can accept a length unit or percentage unit value If you use a length unit, be sure to use a relative unit such as ems or a percentage unit

Indenting The text-indent property indents the first line of a paragraph according to the value you specify You may be tempted to use an absolute measurement such as inches or centimeters with the text-indent property

Indenting Be sure to use a relative length unit or a percentage unit in order to allow the indent to scale according to the element’s font

Text Alignment You have seen how to align text horizontally using the text-align property Although the examples you have seen have been with inline styles, you can also use the text-align property with selectors

Text Alignment The vertical-align property is a little more complicated in that it changes the vertical alignment of an element in relation to its parent element

Text Alignment One common use of the vertical-align property is to adjust the position of images, such as toolbar buttons, that are placed inside a line of text

Setting Font Properties

Font Name The font-family property is a critical font property because it sets the font that an element displays When you select a font for an element, be sure to use a font that you know is installed on a user’s computer

Font Name Your best bet is to assign a list of font names to the font-family property, separated by commas Generic font families represent the five major font families available in typography: serif, sans serif, cursive, fantasy, and monospace

Font Size You have seen examples of how to specify font size using the font-size property When specifying font size, be sure to use a relative length unit such as ems or a percentage unit

Font Size Alternately, you can use one of the following predefined values to set font size: xx-small, x-small, small, medium, large, x-large, xx-large, smaller, or larger

Font Size

Font Appearance In addition to the font family and the font size, you can change the appearance of a font using the font-style, font-variant, and font-weight properties The font-style property allows you to make text italicized or oblique, which is a slanted font, similar to an italicized font

The font Shorthand Property Using the font shorthand property, you can set values for all of the font properties in a single declaration

The font Shorthand Property The values for the font property must be set in the following order: font-style (optional) font-weight (optional) font-variant (optional) font-size (required) line-height (optional) font-family (required)

Validating Style Sheets The W3C offers a utility, the W3C CSS Validation Service, for validating CSS code The W3C CSS Validation Service upload is primarily used for external style sheets

Validating Style Sheets You can download a copy of the utility or validate your CSS code online, the same as you validate XHTML code with the W3C Markup Validation Service

Resources Slides were adapted from the following text & companion lectures: XHTML, Comprehensive First Edition Dan Gosselin Published by Course Technology (2004)

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