In the following code, why does the ul element loose its background color when the child elements are floated?
I remember reading something about floats causing this, but I cannot remember.
(JSFiddle)
ul {
  padding-left: 0;
  background-color: #036;
}
ul li {
  float: left;
}<div id="nav">
  <ul>
    <li class="active"><a href="#">Home</a></li>
    <li><a href="#">Services</a></li>
    <li><a href="#">About Us</a></li>
    <li><a href="#">Contact Us</a></li>
  </ul>
</div> 
    