css3，新增的calc函数
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
<link rel="stylesheet" href="main.css">
<style>
.box {
width: 200px;
height: 100px;
border: 1px solid red;
}
.box>div {
margin: 5px;
display: inline-block;
width: calc(50% - 15px);
height: calc(100% - 15px);
border: 1px solid darkgray;
}
</style>
</head>
<body>
<div class="box">
<div></div>
<div></div>
</div>
</body>
</html>
