HTML进行分类设置和布局
对 HTML 进行分类（设置类），使我们能够为元素的类定义 CSS 样式。
为相同的类设置相同的样式，或者为不同的类设置不同的样式。
London London is the capital city of England. It is the most populous city in the United Kingdom, with a metropolitan area of over 13 million inhabitants. Standing on the River Thames, London has been a major settlement for two millennia, its history going back to its founding by the Romans, who named it Londinium.
实例
<!DOCTYPE html>
<html>
<head>
<style>
.cities {
background-color:black;
color:white;
margin:20px;
padding:20px;
}
</style>
</head>
<body>
<div class="cities">
<h2>London</h2>
<p>
London is the capital city of England.
It is the most populous city in the United Kingdom,
with a metropolitan area of over 13 million inhabitants.
</p>
</div>
</body>
</html>
分类块级元素
HTML <div> 元素是块级元素。它能够用作其他 HTML 元素的容器。
设置 <div> 元素的类，使我们能够为相同的 <div> 元素设置相同的类：
London London is the capital city of England. It is the most populous city in the United Kingdom, with a metropolitan area of over 13 million inhabitants. Standing on the River Thames, London has been a major settlement for two millennia, its history going back to its founding by the Romans, who named it Londinium.
Paris Paris is the capital and most populous city of France. Situated on the Seine River, it is at the heart of the 蝜e-de-France region, also known as the r間ion parisienne. Within its metropolitan area is one of the largest population centers in Europe, with over 12 million inhabitants.
Tokyo Tokyo is the capital of Japan, the center of the Greater Tokyo Area, and the most populous metropolitan area in the world. It is the seat of the Japanese government and the Imperial Palace, and the home of the Japanese Imperial Family. The Tokyo prefecture is part of the world's most populous metropolitan area with 38 million people and the world's largest urban economy.
实例
<!DOCTYPE html>
<html>
<head>
<style>
.cities {
background-color:black;
color:white;
margin:20px;
padding:20px;
}
</style>
</head>
<body>
<div class="cities">
<h2>London</h2>
<p>London is the capital city of England.
It is the most populous city in the United Kingdom,
with a metropolitan area of over 13 million inhabitants.</p>
</div>
<div class="cities">
<h2>Paris</h2>
<p>Paris is the capital and most populous city of France.</p>
</div>
<div class="cities">
<h2>Tokyo</h2>
<p>Tokyo is the capital of Japan, the center of the Greater Tokyo Area,
and the most populous metropolitan area in the world.</p>
</div>
</body>
</html>
分类行内元素
HTML <span> 元素是行内元素，能够用作文本的容器。
设置 <span> 元素的类，能够为相同的 <span> 元素设置相同的样式。
实例
<!DOCTYPE html>
<html>
<head>
<style>
span.red {color:red;}
</style>
</head>
<body>
<h1>My <span class="red">Important</span> Heading</h1>
</body>
</html>
网站常常以多列显示内容（就像杂志和报纸）。
City Gallery London Paris Tokyo London London is the capital city of England. It is the most populous city in the United Kingdom, with a metropolitan area of over 13 million inhabitants. Standing on the River Thames, London has been a major settlement for two millennia, its history going back to its founding by the Romans, who named it Londinium.
使用 <div> 元素的 HTML 布局
注释：<div> 元素常用作布局工具，因为能够轻松地通过 CSS 对其进行定位。
这个例子使用了四个 <div> 元素来创建多列布局：
实例
<body> <div id="header"> <h1>City Gallery</h1> </div> <div id="nav"> London<br> Paris<br> Tokyo<br> </div> <div id="section"> <h1>London</h1> <p> London is the capital city of England. It is the most populous city in the United Kingdom, with a metropolitan area of over 13 million inhabitants. </p> <p> Standing on the River Thames, London has been a major settlement for two millennia, its history going back to its founding by the Romans, who named it Londinium. </p> </div> <div id="footer"> Copyright W3School.com.cn </div> </body>
CSS：
<style>
#header {
background-color:black;
color:white;
text-align:center;
padding:5px;
}
#nav {
line-height:30px;
background-color:#eeeeee;
height:300px;
width:100px;
float:left;
padding:5px;
}
#section {
width:350px;
float:left;
padding:10px;
}
#footer {
background-color:black;
color:white;
clear:both;
text-align:center;
padding:5px;
}
</style>
使用 HTML5 的网站布局
HTML5 提供的新语义元素定义了网页的不同部分：
HTML5 语义元素
这个例子使用 <header>, <nav>, <section>, 以及 <footer> 来创建多列布局：
实例
<body> <header> <h1>City Gallery</h1> </header> <nav> London<br> Paris<br> Tokyo<br> </nav> <section> <h1>London</h1> <p> London is the capital city of England. It is the most populous city in the United Kingdom, with a metropolitan area of over 13 million inhabitants. </p> <p> Standing on the River Thames, London has been a major settlement for two millennia, its history going back to its founding by the Romans, who named it Londinium. </p> </section> <footer> Copyright </footer> </body>
CSS
<style>
header {
background-color:black;
color:white;
text-align:center;
padding:5px;
}
nav {
line-height:30px;
background-color:#eeeeee;
height:300px;
width:100px;
float:left;
padding:5px;
}
section {
width:350px;
float:left;
padding:10px;
}
footer {
background-color:black;
color:white;
clear:both;
text-align:center;
padding:5px;
}
使用表格的 HTML 布局
注释：<table> 元素不是作为布局工具而设计的。
<table> 元素的作用是显示表格化的数据。
使用 <table> 元素能够取得布局效果，因为能够通过 CSS 设置表格元素的样式：
实例
<body>
<table class="lamp">
<tr>
<th>
<img src="/images/lamp.jpg" alt="Note" style="height:32px;width:32px">
</th>
<td>
The table element was not designed to be a layout tool.
</td>
</tr>
</table>
</body>
CSS
<style>
table.lamp {
width:100%;
border:1px solid #d4d4d4;
}
table.lamp th, td {
padding:10px;
}
table.lamp td {
width:40px;
}
</style>
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