<html>
<head>
<style>
body {
  margin: 0px;
  padding: 0px;
}

#logo {
  background-color: green;
  border-top: 1px solid white;
}

h1 {
  margin-top: 50px;
  margin-bottom: 50px;
  padding-top: 20px;
  padding-bottom: 20px;
  font-size: 220%;
  color: white;
}

ul {
  margin: 0;
  padding: 0;
}

li {
  float:left;
  border: 2px solid blue;
  display: block;
  margin: 0px;
}
</style>
</head>
<body>
<div id="logo">
<h1 style="height:30px"></h1>
<div>
<ul>
<li>There should be a gap between this float and the green rectangle above.
</ul>
</div>
</div>

<div style="margin-top:100px;background-color:#dddddd; border:2px solid black">
<div style="float:left;width:2em;height:2em;background-color:white"></div>
<div style="clear:both;margin-top:1em;margin-bottom:1em"></div>
This text should be inside a black rectangle and below the 2em white square.
</div>
<div style="margin-top:1em;background-color:#dddddd; border:2px solid black">
<div style="float:left;width:2em;height:2em;background-color:white"></div>
<div style="clear:both;margin-top:-1em;margin-bottom:1em"></div>
This text should also be inside a black rectangle and below the 2em white square.
</div>