<!DOCTYPE html>
<style>
body { margin: 0px; }
.float { float: left; width:100px; height:100px; background-color: green }
.normal { width: 100px; height:100px; background-color: green }
#container { width: 200px; height:100px; background-color: red }
.negleft { margin-left: -50px; }
.block { display: block; overflow:hidden; }
</style>
<p>There should be no red.</p>
<div id="container">
  <div class="float"></div>
  <div class="block normal negleft"></div>
</div>
