height는 임의로 지정
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
.all::after{clear: both; content: ''; display: block;}
.box1{border: 2px solid purple; width: 50%; height: 180px; float: left;
background-color: pink; box-sizing: border-box;}
.box2{border: 2px solid orange; width: 50%; height: 180px; float: right;
background-color: tan; box-sizing: border-box;}
</style>
</head>
<body class="all">
<div class="box1"></div><div class="box2"></div>
</body>
</html>