Chapter 3 CSS
Vacabulary CSS: 层叠样式表 Syntax: 语法 Selector: 选择器 filter ：滤镜 / 过滤器 background: 背景 property: 属性
Outline 1. What is CSS? 2. A Brief History of CSS 3. Why to use Styles? 4. Syntax 5. Cascading Order 6. Examples of Properties 7. Limitations 8. CSS variations
What is CSS? CSS stands for Cascading Style Sheets Styles define how to display (X)HTML elements Styles are normally stored in Style Sheets Multiple style definitions will cascade into one
A Brief History of CSS Style sheets have existed since the beginnings of SGML in the 1970s As HTML grew, it came to encompass a wider variety of stylistic capabilities Nine different style sheet languages were proposed to the W3C Two were chosen as the foundation for CSS: CHSS and Stream-based Style Sheet Proposal CSS level 1 – 1996; CSS level 2 – 1997 Difficulties with adoption
Why to use Styles? Documents written with CSS are –more flexible –short –clear Basic formating tool Easy multiple document managment Save time by using selector classes New opportunities in formating WebpageStructure(X)HTML Style- formatting CSS
Basic Syntax Made up of three parts: selector {property: value} The selector is normally the HTML element/tag you wish to define The property is the attribute you wish to change Every property has the value
Syntax If the value is multiple words, put quotes around the value p {font-family: "sans serif"} To make the style definitions more readable, you can describe one property on each line p{ text-align: center; text-align: center; color: black; color: black; font-family: arial font-family: arial}
Grouping h1,h2,h3,h4,h5,h6{ color: green } All header elements will be displayed in green text color This is header h1 This is header h2 This is header h3 This is header h4
The class Selector With the class selector you can define different styles for the same type of HTML element. p.right {text-align: right} p.center {text-align: center} Using the class argument in (X)HTML: This paragraph will be right-aligned. This paragraph will be right-aligned. This paragraph will be center-aligned. This paragraph will be center-aligned.
Text color <html><head> h1 {color: green} h2 {color: #dda0dd} h2 {color: #dda0dd} p {color: rgb(0,0,255)} p {color: rgb(0,0,255)}</style></head><body> This is header 1 This is header 1 This is header 2 This is header 2 This is a paragraph This is a paragraph </body></html> This is header 1 This is header 2 This is a paragraph
Inserting Style sheet
Cascading order 1. Browser default 2. External style sheet inside external *.css file 3. Internal style sheet inside the tag 4. Inline style inside an HTML element
External Style Sheet Each webpage must link to the style sheet using the tag Browser reads styles definitions from mystyle.css file <head> </head>
Internal Style Sheet Internal Style Sheet Should be used when a single document has a unique style Defined in the head section by using the tag <head> hr {color: sienna} p {margin-left: 20px} body {background-image: url("images/back40.gi f")} </style></head>
Multiple Style Sheets An internal style sheet has following properties for the h3 selector: h3 { text-align: right; font-size: 20pt } External style sheet has these: h3 { color: red; text-align: left; font-size: 8pt } Your Web Browser has default formatting: h3 { color: black; font size: 10pt } What will be the format of tag? o color: red; o text-align: right; o font-size: 20pt
Examples
Background: Control over the background color of an element set an image as the background, repeat a background image background-color –color-rgb color-hex color-name background-image –url(URL) none background-repeat –repeat repeat-x repeat-y no-repeat
Text:colordirection –ltr rtl word spacing –normal length text-decoration –none underline overline line-through blink text-align –left right center justify
Font: font-family family-name generic-family family-name generic-familyfont-size –xx-small x-small small –/etc./ font-weigh –normal bold bolder lighter 100
Dimension
List: <head> ul{ list-style-image: url('arrow.gif') }</style></head><body><ul> Coffee Coffee Tea Tea Coca Cola Coca Cola </ul></body>
CSS Limitations Some noted disadvantages of using "pure" CSS include –Inconsistent browser support –Inconsistent browser support –Absence of expressions –Absence of expressions –Lack of Variables –Lack of Variables –Lack of multiple backgrounds per element –Lack of multiple backgrounds per element –Control of Element Shapes –Control of Element Shapes
CSS level 1 The first CSS specification to become an official W3C Recommendation is CSS level 1, published in December Among its capabilities are support for: –Font properties such as typeface and emphasis –Color of text, backgrounds, and other elements –Text attributes such as spacing between words, letters, and lines of text –Alignment of text, images, tables and other elements –Margin, border, padding, and positioning for most elements –Unique identification and generic classification of groups of attributes The W3C maintains the CSS1 Recommendation.
CSS level 2 published as a Recommendation in May includes a number of new capabilities –absolute, relative, and fixed positioning of elements –the concept of media types –bidirectional text –new font properties such as shadows The W3C maintains the CSS2 Recommendation. CSS level 2 revision 1 or CSS 2.1 fixes errors in CSS2 –returned to Candidate Recommendation status on 19 July 2007