See and adapt:
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Split 50/50 Vertically</title>
<style>
div {
float: left;
width: 50%;
}
</style>
</head>
<div style="background-color:#9F6">left</div>
<div style="background-color:#F60">right</div>
<body>
</body>
</html>