height:100%

 1 <!DOCTYPE html>
 2 <html lang="en">
 3 <head>
 4     <meta charset="UTF-8">
 5     <title>Document</title>
 6 </head>
 7 <style>
 8 *{
 9     margin:0px; padding:0px;
10 }
11 body{height:100%;}
12 ul{overflow:hidden;}
13 .li1{
14     float:left;
15     width:40%;
16     height:100%;
17     position:absolute;
18     background-color:#0f0;
19 }
20 .li2{
21     width:60%;
22     height:500px;
23     float:right;
24     background-color:#f00;
25 }
26 </style>
27 <body>
28     <div class="box">
29         <ul>
30             <li class="li1"></li>
31             <li class="li2"></li>
32         </ul>
33     </div>
34 </body>
35 </html>