​x
 
<!DOCTYPE html>
<html>
<head>
<style>
h1 {
  text-decoration: underline;
  text-decoration-thickness: auto;  
}
​
h2 {
  text-decoration: underline;
  text-decoration-thickness: 5px;  
}
​
h3 {
  text-decoration: underline;
  text-decoration-thickness: 50%;    
}
​
/* 使用简写属性 */
h4 {
  text-decoration: underline solid red 50%;    
}
</style>
</head>
<body>
​
<h1>这是标题 1</h1>
<h2>这是标题 2</h2>
<h3>这是标题 3</h3>
<h4>这是标题 4</h4>
​
</body>
</html>
​