1/*this is how to make height: x% work in HTML. you have to set the
2height of the body to 100vh or nothing will happen regarding height
3of the element.*/
4
5<html>
6 <head>
7 <style>
8 body {
9 height: 100vh;
10 }
11 #box {
12 width: 20px;
13 height: 100%;
14 }
15 </style>
16 </head>
17
18 <body>
19 <div id = 'box'></div>
20 </body>
21</html>