<!doctype html>
<head>
<style>
.float { float:left; height:100px; width:100px; background-color:green }
.half { display:inline-block; width:50px; background-color:lime; height:50px }
.bordered { width:150px; border:2px solid black; }
.margins { height:50px; margin-bottom:50px }
</style>
<body>

<div class="bordered">
<div class="float"></div>
<div class="margins"></div><div class="half"></div><div class="half"></div>
</div>