effect:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<title>Page Title</title>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" type="text/css" media="screen" href="main.css" />
<script src="main.js"></script>
</head>
<style>
*{ margin: 0;padding: 0;}
.content{width: 1320px;height: auto;margin: 20px auto;}
.fl{float: left;width: 276px;height: 460px;background: #abcdef;}
.fr{float: right;}
.fr ul{width: 1044px;height: 460px;display: flex;flex-wrap: wrap;justify-content: space-between;}
.fr ul li{float: left;border: 1px solid #ccc;list-style: none;}
.fr ul .con1{width: 270px;height: 230px;}
.fr ul .con2{width: 490px;height: 230px;}
</style>
<body>
<div class="content">
<div class="fl"></div>
<div class="fr">
<ul>
<li class="con1">1</li>
<li class="con1">2</li>
<li class="con2">3</li>
<li class="con2">4</li>
<li class="con1">5</li>
<li class="con1">6</li>
</ul>
</div>
</div>
</body>
</html>