我直接写了个案例，先看下效果图：
下面是html代码：
<!DOCTYPE html>
<html><head><meta charset="utf-8" /><title>机构动态</title><style type="text/css">*{margin:0px;padding:0px; }.test_m ul {margin: 20px;width: 630px;overflow:hidden;border-top:1px solid black;}.test_m ul li{padding: 10px 20px 11px 20px;box-sizing: border-box;float: left;width: 315px;height: 111px;list-style: none;}.test_m ul li:nth-child(2n+1){border:1px solid black;border-top:0;}.test_m ul li:nth-child(2n){border-bottom:1px solid black;border-right:1px solid black;}</style></head><body><div class="test_m"><ul><li>菜单1</li><li>菜单2</li><li>菜单3</li><li>菜单4</li></ul></div></body>
</html>
