1．2 跟css有關的標記，指令1．2．1 link<link rel="stylesheet" type="text/css" href="sheet1.css" media="all" />link標記的用意是允許將html與其他文檔相關聯。Css用link將css文檔與html文檔想關聯。Css文檔雖然不是html的一部分，但是被html使用，從外部style sheets引入它。Link在head元素內，但是不能放在任意head子元素的內部，比如title。Css文檔的后綴名雖然不要求，但是有些瀏覽器不能識別非“.css”的文件。Link的屬性：rel：代表relation，設為stylesheet。type：描述數據的類型，設為text/css，告訴瀏覽器style sheet是css格式的。以后還會有其他的style sheet，比如xsl。href：style sheet的url。Media：指定style sheet的使用范圍。下列大多數值還不被任何瀏覽器支持，常用的是all，print，screen。Opera支持projection。可以為media指定多個值，比如media="screen, projection"all Use in all presentational media.aural Use in speech synthesizers, screen readers, and other audio renderings of the document.braille Use when rendering the document with a Braille device.embossed Use when printing with a Braille printing device.handheld Use on handheld devices like personal digital assistants or web-enabled cell phones.print Use when printing the document for sighted users and also when displaying a "print preview" of the document.projection Use in a projection medium, such as a digital projector used to present a slideshow when delivering a speech.screen Use when presenting the document in a screen medium like a desktop computer monitor. All web browsers running on such systems are screen-medium user agents.tty Use when delivering the document in a fixed-pitch environment like teletype printers.tv Use when the document is being presented on a television.Title：利用title定義多個css文檔相互替換的關系。比如存在如下定義： <link rel="stylesheet" type="text/css" href="sheet1.css" title="Default" /><link rel="alternate stylesheet" type="text/css" href="bigtext.css" title="Big Text" /><link rel="alternate stylesheet" type="text/css" href="zany.css" title="Crazy colors!" />那么能同時支持多個css定義的瀏覽器中會有如下表現：還可以通過將title設定為相同的value來分組： <link rel="stylesheet" type="text/css" href="sheet1.css" title="Default" media="screen" /> <link rel="stylesheet" type="text/css" href="print-sheet1.css" title="Default" media="print" /> <link rel="alternate stylesheet" type="text/css" href="bigtext.css" title="Big Text" media="screen" /> <link rel="alternate stylesheet" type="text/css" href="print-bigtext.css" title="Big Text" media="print" /> 上面的表述意為：css被title分為兩組，default和Big Text。又每一組又被分為print和screen。如果有多個link元素，那么只有rel等于stylesheet的link可用。如果可用的link有多個，就會將它們同時作用于html文檔，如下：<link rel="stylesheet" type="text/css" href="basic.css" /><link rel="stylesheet" type="text/css" href="splash.css" />1．2．2 stylestyle是引入style sheet最通用的方式。<style type="text/css">type：style總是使用type屬性，當使用css時，type的值是“text/css”。Media：與link中一樣。style以<style type="text/css">開頭，以</style>結束，中間是多個styles。這些styles或者指向style sheet文檔，或者以內嵌的方式表達。Style元素可以包含多個styles，也可以通過@import指令引入多個指向外部style sheet的鏈接。1．2．3 @import指令用法： <style type="text/css">@import url(styles.css); /* @import comes first */@import url(blueworld.css);@import url(zany.css);h1 {color: gray;}</style>可見其作用類似link，l通知瀏覽器將外部style sheet載入。l并且可以載入多個style sheet。區別是l位置與語法不同。@import被包含在style元素中，并且必須在其他css規則之前。l每一個import的style sheet都會被使用，沒有替代規則。相對于link的media屬性，import有：@import url(sheet2.css) all;@import url(blueworld.css) screen;@import url(zany.css) projection, print;@import的重要用途：在導入的某個style sheet A中，A需要也使用外部的style sheet，這時link元素顯然無用。比如css文檔中，是不可能出現link元素的，這時使用@import，如下：@import url(http://example.org/library/layout.css);@import url(basic-text.css);@import url(printer.css) print;body {color: red;}h1 {color: blue;}1．3 與老版本瀏覽器的兼容問題瀏覽器對不能識別的tag一律忽略。但是如果瀏覽器不能識別style元素，style會以普通文本的形式出現在網頁的最上面。解決方案：在style里面加上注釋符號，這樣舊版本的瀏覽器不會以文本方式顯示，新版本瀏覽器可以正確使用style元素。具體如下：<style type="text/css"><!--@import url(sheet2.css);h1 {color: maroon;}body {background: yellow;}--></style>1．4 css中的注釋css的注釋類似c：/* This is a CSS1 comment */Comments can span multiple lines, just as in C :/* This is a CSS1 comment, and itcan be several lines long withoutany problem whatsoever. */但是注意：css的注釋不能被嵌套。1．5內聯風格inline style將style放到html元素描述的地方，就是inline style<p style="color: gray;">The most wonderful of all breakfast foods is the waffle--a ridged and cratered slab of home-cooked, fluffy goodness...</p>這個style屬性是一個新屬性，可以用到出現body元素中的所有元素上。可以看到style的值是一個字符串，使用和css一樣的語法。但是這個字符串只能是一個風格聲明塊declaration block。不能將@import和css規則放到這個字符串中。就是說只能放css文檔中出現在花括號中的文本。注意：inline style不被推薦使用，在xhtml1.1中inline style是反對的deprecated。因為，它顯示違背數據和顯示分離的原則。這個原則也是使用css的原因。2 selectorcss核心的特點是將規則應用到元素集上的能力。Css2規范種關于selector的部分，http://www.w3.org/TR/REC-CSS2/selector.html css的模式匹配pattern matching規則（css規范，地址如上）： PatternMeaningDescribed in section*Matches any element.Universal selectorEMatches any E element (i.e., an element of type E).Type selectorsE FMatches any F element that is a descendant of an E element.Descendant selectorsE > FMatches any F element that is a child of an element E.Child selectorsE:first-childMatches element E when E is the first child of its parent. The :first-child pseudo-classE:link E:visited Matches element E if E is the source anchor of a hyperlink of which the target is not yet visited (:link) or already visited (:visited). The link pseudo-classesE:active E:hover E:focus Matches E during certain user actions. The dynamic pseudo-classes E:lang(c) Matches element of type E if it is in (human) language c (the document language specifies how language is determined). The :lang() pseudo-class E FMatches any F element immediately preceded by an element E.Adjacent selectors E[foo]Matches any E element with the "foo" attribute set (whatever the value). Attribute selectors E[foo="warning"]Matches any E element whose "foo" attribute value is exactly equal to "warning". Attribute selectors E[foo~="warning"]Matches any E element whose "foo" attribute value is a list of space-separated values, one of which is exactly equal to "warning". Attribute selectors E[lang|="en"]Matches any E element whose "lang" attribute has a hyphen-separated list of values beginning (from the left) with "en". Attribute selectors DIV.warningHTML only. The same as DIV[class~="warning"]. Class selectorsE#myidMatches any E element ID equal to "myid".ID selectors
還可以通過將title設定為相同的value來分組：
