W3Schools 代码 - Tryit

<!DOCTYPE html>
<html>
<head><meta http-equiv="content-security-policy" content="script-src 'none'">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<style>
* {
  box-sizing: border-box;
}
.menu {
  float:left;
  width:20%;
  text-align:center;
}
.menu a {
  background-color:#e5e5e5;
  padding:8px;
  margin-top:7px;
  display:block;
  width:100%;
  color:black;
}
.main {
  float:left;
  width:60%;
  padding:0 20px;
}
.right {
  background-color:#e5e5e5;
  float:left;
  width:20%;
  padding:15px;
  margin-top:7px;
  text-align:center;
}

@media only screen and (max-width:620px) {
  .menu, .main, .right {
    width:100%;
  }
}
</style>
</head>
<body style="font-family:Verdana;color:#aaa;">

<div style="background-color:#e5e5e5;padding:15px;text-align:center;">
  <h1>Hello World</h1>
</div>

<div class="main">
    <h2>Lorum Ipsum</h2>
    <p>Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh euismod tincidunt ut laoreet dolore magna aliquam erat volutpat.</p>
  </div>

<div class="right">
    <h2>About</h2>
    <p>Lorem ipsum dolor sit amet, consectetuer adipiscing elit.</p>
  </div>
</div>

<div style="background-color:#e5e5e5;text-align:center;padding:10px;margin-top:7px;">copyright w3schools</div>

</body>
</html>