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CSS - Cascading Style Sheets

CSS - Cascading Style Sheets. What is CSS ?. css defines how to display an html document (fonts, colors, layouts etc.) were added to HTML 4.0 specification to solve a problem usually css styles are specified in an external file

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CSS - Cascading Style Sheets

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  1. CSS - Cascading Style Sheets

  2. What is CSS ? • css defines how to display an html document (fonts, colors, layouts etc.) • were added to HTML 4.0 specification to solve a problem • usually css styles are specified in an external file • enables developers to change the layout and look of all documents in a web site by just editing a single file

  3. Need for CSS • HTML was intended to define the structure of a document (i.e. headings, paragraphs, tables etc.), not the formatting of an element • when style attributes like font, color, background etc. were introduced, maintaining a large web page in which formatting/style information was scattered all over the document became a nightmare for web developers • so, HTML 4.0 allowed formatting information to be removed from the document and placed separately (in .css files)

  4. A simple CSS example body {background-color: #aabbcc} h1 {font-style: italic; font-size: 36pt} h2 {color: blue} p {margin-left: 50px} • it specifies that: • the <body> tag should have a background color of #aabbcc • the <h1> heading tag should use an italic font of size 36pt • the <h2> heading tag should use a blue color for displaying text • a paragraph <p> tag should start at an offset of 50 pixels on the left

  5. CSS syntax rules selector { property: value; property: value; …} • where selector can be: • a tag name; ex.: p { font-family: sans-serif } • a group of tags; ex.: h1, h2, h3, h4, h5, h6 { color: red } • a class name (with or without a tag name): p.right { text-align: right } .right { text-align: right } … in html document: <p class=“right”>Right aligned text</p> • an ID (with or without a tag name): div#green { color: green } #green { color: green } … in html document: <div id=“green”>Green div…</div> • pseudo-classes and pseudo-elements

  6. Pseudo-classes • syntax: selector:pseudo-class {property: value; …} selector.class:pseudo-class {property: value; …} • list of pseudo-classes: • anchor pseudo-classes: a:link {color:#FF0000}      /* unvisited link */a:visited {color:#00FF00}  /* visited link */a:hover {color:#FF00FF}  /* mouse over link */a:active {color:#0000FF}  /* selected link */ • :first-child: matches an element that is the first child of any other element;ex.: p:first-child { color: blue } • > selector:first-child: matches an element that is the first child of a specific element; ex.: p > i:first-child { color: blue} • :lang: adds a style to an element with a specific lang attribute • :active: adds a style to an element that has keyboard input focus

  7. Pseudo-elements • syntax: selector:pseudo-element {property: value; …} selector.class:pseudo-element {property: value; …} • list of pseudo-elements: • :first-letter – adds style to the first character of a text div:first-letter { font-size: xx-large; } • :first-line – adds style to the first line of a text div:first-line { color: red } • :before – adds content before an element h1:before { content: url(smiley.jpg)} • :after – adds content after an element h1:after { content: url(smiley.jpg)}

  8. Adding style sheets to a document • external style sheet: <head> <link rel=“stylesheet” type=“text/css” href=“style.css”> </head> • internal style sheet: <head> <style type=“text/css”> p { margin-left: 10px } </style> </head> • inline style sheet: <p style=“color: red; margin-left: 10px}

  9. Multiple style sheets • if multiple style sheets are defined, their priority is (ascending order): 1) browser default 2) external style sheet 3) internal style sheet 4) inline style

  10. Background properties

  11. Background CSS example div {background-color:#0f0f0f; background-image:url(‘back.jpg');background-repeat:repeat-x;background-position:top right; }

  12. Border and outline properties

  13. Border CSS example div { border-top-style: solid; border-bottom-style: solid; border-left-style: dotted; border-right-style: dotted; border-width: 2px; border-color: #00ff00; }

  14. Dimension properties

  15. Font properties

  16. Font CSS example p, div { font-family:”Times New Roman”, Arial, Serif; font-style: italic; font-size: 12px; }

  17. List properties

  18. List CSS example ul { list-style-type: circle; list-style-position: inside; }

  19. Margin and padding properties

  20. Margin CSS example div { margin-top: 100px; margin-bottom: 100px; margin-left: 5%; margin-right: 5%; }

  21. Positioning properties

  22. Table properties

  23. Text properties

  24. Text CSS example h1 { color: #00ddee; text-align: justify; text-decoration: underline; text-shadow: 10; }

  25. The CSS box model • each HTML element is a “box” from CSS perspective; it has a margin, border, padding and content

  26. The CSS Box model (2) • Margin: clears an area around the border; does not have a background color, is completely transparent • Border: lies around content and padding; has the background color of the box • Padding: clears an area around the content; has the background color of the box • Content: the actual content (text) of the box • the height and width attributes do not specify the total height and width of the HTML element; they are calculated by: Total width=width+left padding+right padding+left border+ right border+left margin+right margin Total height=height+top padding+bottom padding+top border+ bottom border+top margin+bottom margin

  27. Displaying and visibility • hiding an element with consuming space: visibility: hidden; • hiding an element without consuming space: display: none; • html elements are displayed as: • block – element takes the full width available and has a line break before and after it (e.g. h1, p, div) • inline – element takes as much width as necessary and does not force line breaks (e.g. a, span) • set the display mode with the display property (e.g. display: inline; display: block;) • make an image transparent: opacity: x – on Firefox, x between 0.0 and 1.0 filter:alpha(opacity=x) – on IE, x between 0 and 100.

  28. Positioning • static positioning: the default mode; a static element is positioned according to the normal flow of the page; • fixed positioning: element will not move even if the window is scrolled (position: fixed; top: 20px; right: 40px); elements are removed from the normal flow and can overlap other elements • relative positioning: element is positioned relative to its normal position; element can be moved and overlap other elements , but the reserved space form the element is preserved in the normal flow (position: relative) • absolute positioning: element is positioned relative to the first parent element that has a position other then static (if none, <html>); elements are removed from the normal flow and can overlap other elements; (position: absolute) • z-index property defines the stack order of an element

  29. Floating • with floating, an html element can be pushed left or right allowing other elements to wrap around it • html elements can float horizontally left or right (not vertically) • configured using the the float: left | right | none | inherit display property

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