代码示例:(标识:css_layout_webpage)
<!DOCTYPE html>
<html>
<head>
<style>
* {
  box-sizing: border-box;
}

body {
  margin: 0;
}

.header {
  background-color: #2196F3;
  color: white;
  text-align: center;
  padding: 15px;
}

.footer {
  background-color: #444;
  color: white;
  padding: 15px;
}

.topmenu {
  list-style-type: none;
  margin: 0;
  padding: 0;
  overflow: hidden;
  background-color: #777;
}

.topmenu li {
  float: left;
}

.topmenu li a {
  display: inline-block;
  color: white;
  text-align: center;
  padding: 16px;
  text-decoration: none;
}

.topmenu li a:hover {
  background-color: #222;
}

.topmenu li a.active {
  color: white;
  background-color: #4CAF50;
}

.column {
  float: left;
  padding: 15px;
}

.clearfix::after {
  content: "";
  clear: both;
  display: table;
}

.sidemenu {
  width: 25%;
}

.content {
  width: 75%;
}

.sidemenu ul {
  list-style-type: none;
  margin: 0;
  padding: 0;
}

.sidemenu li a {
  margin-bottom: 4px;
  display: block;
  padding: 8px;
  background-color: #eee;
  text-decoration: none;
  color: #666;
}

.sidemenu li a:hover {
  background-color: #555;
  color: white;
}

.sidemenu li a.active {
  background-color: #008CBA;
  color: white;
}
</style>
</head>
<body>

<ul class="topmenu">
  <li><a href="#home" class="active">Home</a></li>
  <li><a href="#news">News</a></li>
  <li><a href="#contact">Contact</a></li>
  <li><a href="#about">About</a></li>
</ul>

<div class="clearfix">
  <div class="column sidemenu">
    <ul>
      <li><a href="#flight">The Flight</a></li>
      <li><a href="#city" class="active">The City</a></li>
      <li><a href="#island">The Island</a></li>
      <li><a href="#food">The Food</a></li>
      <li><a href="#people">The People</a></li>
      <li><a href="#history">The History</a></li>
      <li><a href="#oceans">The Oceans</a></li>
    </ul>
  </div>

  <div class="column content">
    <div class="header">
      <h1>The City</h1>
    </div>
    <h1>Shanghai</h1>
    <p>Shanghai is one of the four direct-administered municipalities of the People's Republic of China. Welcome to Shanghai!
</p>
    <p>You will learn more about responsive web pages in a later chapter.</p>
  </div>
</div>

<div class="footer">
  <p>Footer Text</p>
</div>

</body>
</html>
运行结果: