<!DOCTYPE html>
<html>
<head>
<style type='text/css'>
.container {
border: 1px solid red;
overflow: auto;
margin: 10px 0;
}
.container .LC {
width: 50%;
margin: 0 -1em;
float: left;
background-color: yellow;
border-right: 1em solid blue;
}
.container .RC {
width: 50%;
float: left;
background-color: cyan;
border-left: 1em solid blue;
}
.small {
width: 60%;
margin: 10px auto;
}
</style>
</head>
<body>
<div class="container small">
<div class="LC">Left</div>
<div class="RC">Right</div>
</div>
</body>
</html>