<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
</head>
<!-- 第一种方法的样式，利用盒子的border-bottom实现 -->
<style>
#box {
width: 100%;
height: 100px;
line-height: 100px;
border: 1px solid #f00;
text-align: center;
}
#span1,#span3 {
width: 40%;
height: 50px;
border-bottom: 1px solid #f00;
}
#span1 {
float: left;
}
#span3{
float: right;
}
</style>
<!-- 第二种方法的样式 -->
<!-- <style>
#box {
height: 30px;
text-align: center;
line-height: 30px;
}
#span2 {
margin: 0 30px;
vertical-align: middle;
}
#span1,
#span3 {
display: inline-block;
width: 200px;
border: 1px solid #f00;
} -->
</style>
<body>
<!-- 不管哪种方法都共用一个HTML样式 -->
<div id="box">
<span id="span1"></span>
<span id="span2">中间</span>
<span id="span3"></span>
</div>
</body>
</html>