1. 1 Cascading Style Sheets (CSS) DBI 2003

2. 2 Overview of CSS

3. 3 Same Page – Different Styles Look at W3C Core Style SamplerW3C Core Style Sampler How is it done?  Style declarations are in a separate file  The HTML (or XML) document has a link to the style sheet You can download and look at the Modernist style sheetModernist The style for the H1 tag, as defined in modernist.css, is shown on the next slide

4. 4 h1{ font-family:Impact, Arial Black, Helvetica Black, sans-serif; font-size-adjust:.46; font-size:2.33em; font-weight:400; font-style:normal; text-decoration:none; word-spacing:normal; letter-spacing:normal; text-transform:none; }

5. 5 What is a Style? Font properties  family, size, weight, style, variant Text properties  color, transform, decoration Background  background-color, background-image, background-repeat, background- attachment, background-position, background Property names appear in red

6. 6 A Style is Also a Layout Text Layout  direction, word-spacing, white-space, letter- spacing, line-height, text-align, text-indent Elements as Boxes  margin-top (-bottom, -left, -right)  padding-top (-bottom, -left, -right)  border-width, border-color, border-style Positioning Boxes  float, clear, display, vertical-align  position, left, top, width, height, overflow, visibility, clip, z-index Property names appear in red

7. 7 How and Where the Style is Described? The style is specified by style rules The style rules appear either in the document or in external files, called style sheets Inside a document, there are inline styles and embedded style sheets External style sheets are either linked or imported

8. 8 Cascading of Styles CSS merges style rules from different places (inline, document-level, imported and linked) Different places may have conflicting style rules The process of merging (“cascading”) styles from different places determines which style rules have priority

9. 9 Overview of the Layout Process in CSS Think of each word as a rectangular box The natural layout of the boxes is  left to right  top to bottom Think of each HTML (or XML) element as a big box that contains smaller boxes (e.g., words)

10. 10 The Layout of Big Boxes Big boxes are also laid out left-to-right, top-to-bottom Inside each big box, the smaller boxes are laid out similarly This is a simplified description of the layout process Actually, there are more options than just the natural document flow

11. 11 Layout in HTML vs. CSS In pure HTML, the only way to control the positions of elements is by using tables  It is cumbersome to control positions in this way  Rendering tables in a browser may take some time (check out this page)this page CSS makes it easy to position elements on a page

12. 12 Relative vs. Absolute In CSS, positions (of boxes) and sizes (of fonts and boxes) could be either relative or absolute In an “absolute” style  Font size is fixed  Sizes and positions of elements are fixed In a “relative” style  you can change the font size  The sizes and positions of elements may change when the size of the window is changed

13. 13 Examples of Relative vs. Absolute www.ynet.co.il (like most newspapers) has an “absolute” designwww.ynet.co.il  Is it possible to change the font size?  Is it possible to view more material if you have a wide screen? www.useit.com has a “relative” designwww.useit.com  You can change the size of the fonts  The width of the two columns is adjusted according to the width of the browser window

14. 14 Design Tip Make your design as “relative” as possible, since  The Web is not WYSIWYG because of the variability in supported platforms 21-inch monitor Laptop Hand-held device In other words, site designers and page authors should not try to fully control how their pages will be viewed

15. 15 In Particular Site designers and page authors should not override the the style rules of the client (although it can be done)

16. 16 Different Levels of CSS W3C has specifications for CSS Level 1, CSS Level 2 and CSS Level 3 Most recent versions of browsers try to implement CSS Level 2 Hardly any browser implements CSS Level 2 completely and correctly You should try your style sheets on different browsers, especially if you use complex features of CSS

17. 17 Design Tip Design your site so that it will be rendered reasonably well also on browsers that do not support CSS

18. 18 Examples and Resources Suppose you want to fix your logo on the background – look at an exampleexample W3Schools has many simple examples and a good CSS2 referenceW3Schools Many tutorials on the Web (e.g., Mulder's Stylesheets Tutorial)Mulder's Stylesheets Tutorial Eric Costello describes layout techniques using CSS and has links to tutorials and other resources on layout techniquesEric Costello

19. 19 CSS Rules

20. 20 Declarations A declaration consists of a property and one or more values The property is separated from the values by a colon  property1: value1  property2: value1 value2 value3 Slides 5 and 6 list many of (but not all) the properties of CSS See a list of properties and their possible values in W3SchoolsW3Schools

21. 21 Declaration Blocks A declaration block is a list of zero or more declarations that are separated by semicolons: A declaration block usually appears inside a pair of { and } In in-line styles, a declaration block appears inside a pair of double quotes  “declaration block” property1: value1; property2: value1 value2 value3;…

22. 22 Examples color: red; font-size: 12pt margin-top: auto; margin-right: 100px; margin-bottom: 10%; margin-left: 5mm Alternatively, we can set all four margins in one declaration as follows margin: auto 100px 10% 5mm

23. 23 Inline Styles In an inline style, the declaration block appears as the value of the attribute style (conforming to XML syntax) This text will be shown in italic green and the size will be 1.5 times the current font size

24. 24 CSS Rules A rule has the following form selector {declaration block} The selector determines when the rule is applied The following rule applies to text that is inside a tag P {color: green; font-size: 1.5em; font-style: italic}

25. 25 Several Kinds of Selectors Universal Selector Type Selectors Descendant Selectors Child Selectors Adjacent-Sibling Selectors Attribute Selectors Class Selectors ID Selectors Pseudo-Class Selectors Pseudo-Element Selectors Selectors can be grouped

26. 26 Type Selector A type selector is the name of an element type A type selector matches every instance of the element type What will be the color and the size if the font is inside a element which is inside a element? P {color: green; font-size: 1.5em; font-style: italic} DIV {color: red; font-size: 16px}

27. 27 Universal Selector The universal selector matches every element type The following rule means that all the text will have a size of 40px * {font-size: 40px}  But even that may not work The following will always work * {font-size: 40px ! important}

28. 28 Class Selectors The definition of the class.... Style rules for the class  P.introductoryparagraph {color: blue} applies to P elements with the class name introductorypargraph .introductoryparagraph {color: blue} applies to any element with the class name introductoryparagraph

29. 29 Class Selectors (cont’d) An element may have more than one class, e.g., This element matches the following selectors P.quote.green P.new P.quote.new.green It does not match P.new.old Few browsers support it

30. 30 ID Selectors IDs are identical to classes, except that there can only be one element with a given ID in a document In the HTML (or XML) document:  In the style sheet:  BODY#introduction {font-size: 1.2em}  #introduction {font-size: 1.2em}

31. 31 Attribute Selectors P[attribute]  matches P when attribute is set to any value P[title=intro] or P[title="intro"] (the quotes are optional)  matches P when its title attribute is set to "intro" P[class~=green]  matches P when the class attribute is set to "green small", "small green", "green", etc.

32. 32 Pseudo-Classes The pseudo-classes :link and :visited are used to define styles for links and visited links :hover is used to define a style for an element when the mouse is over that element :focus is used to define a style when the element is ready to accept input :active is used while an element is being activated by the user (during the time between pressing the mouse button and releasing it or pressing it again in a different place)

33. 33 Examples of Rules for Pseudo-Classes A:link {color: blue} A:visited {color: purple} A:hover {font-size: 1.5em} A:active {color: red} INPUT:focus {background-color: yellow} For links, the order of the rules is important From a usability point of view, it is not recommend to change the default colors of :link and :visited

34. 34 More Examples of Pseudo-Classes Look at the examples in W3SchoolsW3Schools

35. 35 The :first-child Pseudo-Class It is used to denote an element which is the first child of its parent This is the first child of OL – it is matched by the selector LI:first-child This is the second child of OL – it is not matched by the above selector

36. 36 Pseudo-Elements A pseudo-element selector matches part of an element (whereas a pseudo-class selector matches a complete element) :first-line and :first-letter match the first line and the first letter of an element, respectively Examples:  P:first-line {text-transform: capitalize}  P:first-letter {font-size: 48px; color: red}

37. 37 Contextual Selector P B {color: red} The above rule is matched by a B element if that element is nested (at any level) inside a P element

38. 38 Grouping of Selectors The following rule applies to all elements of that match either H1, H2, H3 or P B P B, H1, H2, H3 {font-size: 120%}

39. 39 Example Formatting style with CSS A joke A mama tomato, a papa tomato and a baby tomato are walking down the street. The baby tomato keeps falling behind so the papa tomato goes back, steps on the baby tomato and says, ketchup ("Catch-up!").

40. 40

41. 41 Adding Style <!-- BODY { background-image: url("tomato1.gif"); background-attachment: fixed } H1 { background-color: rgb(100,150,100); color: rgb(250, 200, 250) } P { background-color: yellow; color: purple; font-size: 200% } -->

42. 42

43. 43 Another Example

44. 44 Some more style examples <!-- BODY {font-size: 30} P:first-line {color: #ff0000;font-variant: small-caps} --> <SPAN style="float: left; font-size: 100px; line-height: 90px; width: 60px">T wo cows were walking together in a field. One turns to the other and says, "hey larry are you worried about getting that mad cow disease?" Larry, in a very odd and wacky voice says, "why would I, I'm a chicken?" "why would I, I'm a cow?"

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46. 46 The Sources of Style Sheets

47. 47 Embedded Style Sheets <!-- BODY {color: red} -->... The embedded style sheet appears in the header inside a element. All the text of the style sheet is inside an HTML comment so that browsers that do not support CSS will ignore the text.

48. 48 Inline Styles Any tag, except the tag itself, can have the style attribute For example, the following will define the color of the paragraph to be green and this is green

49. 49 Imported Style Sheets The @import rule imports style rules to the beginning of the style sheet Usage: @import url(nameOfFile.css) Several import rules may appear at the beginning of the style sheet Import rules can appear in embedded style sheets or in external style sheets

50. 50 Linked Style Sheets Links to external style sheets can appear in the header of an HTML page...

51. 51 Inheritance and Cascading

52. 52 Inheritance of Properties If an element does not match any rule for some given property, then the element inherits the computed value for that property from its parent element

53. 53 Example Given the rules:  BODY { font-size: 10pt }  H1 { font-size: 120% } What will be the font size of the EM element? A large heading

54. 54 Cascading Order When several rules define the same property and match the same element, then the cascading order is as follows:  Primary sort: weight and origin  Secondary sort: specificity of selectors  Final sort: order of appearance The cascading order determines which rules applies

55. 55 Weight and Origin Author style sheets override user style sheets User style sheets override default (browser) style sheets ! important declaration overrides normal declaration If both author and user declarations have ! important, the user declarations still override the author declarations (in CSS2, but not in CSS1)

56. 56 Specificity of a Selector Let a be the number of ID attributes in the given selector Let b be the number of attributes and pseudo-classes in the given selector Let c be the number of element names in the given selector Sort the triples (a,b,c) lexicographically) Pseudo-elements are ignored

57. 57 Example Consider the two rules  P {…} .introductory {…} If an element matches both, then the second rule has a higher specificity and overrides the first

58. 58 Order of Appearance If two rules have the same weight, origin and specificity, then the one that appears last in the style sheet overrides the others Rules in imported style sheets are considered to appear before local rules