1. Using Cascading Style Sheets Module B: CSS Structure

2. 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

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

4. 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”

5. 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

6. Internal Style Sheets

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

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

22. 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

23. 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)

24. Background Images

25. 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

26. 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

27. 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

28. 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

29. CSS1 Text Properties

30. 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

31. 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

32. 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

33. 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

34. 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

35. 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

36. 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

37. 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

38. 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

39. 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

40. 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

41. Setting Font Properties

42. 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

43. 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

44. 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

45. 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

46. Font Size

47. 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

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

49. 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)

50. 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

51. 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

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

53. Questions?