重温CSS之文档结构_html/css_WEB-ITnose
出处：http://limits.cnblogs.com
我们来看看几个基本的HTML页面
1 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 2 <html xmlns="http://www.w3.org/1999/xhtml"> 3 <head> 4 <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> 5 <title>文档结构</title> 6 </head> 7 8 <body> 9 <h1 id="CSS规则">CSS规则</h1>10 <p>样式表由一些<strong>样式规则</strong>组成。</p>11 <ul>12 <li>选择器13 14 <ul>15 <li>类选择器</li>16 <li>ID选择器</li>17 <li><em>包含</em>选择器</li>18 </ul>19 <li>属性</li>20 <li>值</li>21 </li>22 </ul>23 </body>24 </html>
显示如下：
文档结构如下图：
特殊性：
规定了不同规则的权重，当多个规则都可用于同一个元素时，权重越高的样式会被优先采用。
h1 {color:red;}/*特殊性=1*/p em{color:blue;}/*特殊性=2*/.divclass{color:yellow;}/*特殊性=10*/p.note em.dark{color:gray;}/*特殊性=22*/#id{color:black;}/*特殊性=100*/
使用!important来标识重要规则，如：p{color:red !important;}，此时color:red将具有最高的权重性，因这样声明的规则将高于访问者本地样式的定义(就是P标签内的定义)，所以!important要谨慎使用。
元素分类：
- 块级元素(display:block)：每个块级元素都从一个新行开始，而且其后的元素也需要另起一行开始标题、段落、表格、层、body等都是块级元素；
- 内联元素(display:inline)：内联元素不需要在新行显示，而且也不强迫其后的元素换行，如a,em,span等都是内联元素，内联元素可以为任何其他元素的子元素；
- 列表项(display:list-item)：只有li元素是默认此类型，此元素的表现形式和列表一样；
- 隐藏元素(display:none)：当某个元素被设置为display:none的时候，浏览器会完全忽略掉此元素，此元素将不会被显示，也不会占据位置。
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