title: Why is background color of #wrapper not showing up behind the left and content columns?
body: <p>Look at the html and css below. I have set the width of the #wrapper to 990 px and complete width of center columns is 960 px. Margin of 15px is there in both sides. So, wrapper div's background color should be showing up there behind the #left and #content divs. However if i set the height of #wrapper it does show the background. But i want it to be shown as full.</p>
  
  <p>I am just a beginner in CSS layouts.</p>
  
  <hr>
  
  <hr>
  
  <pre><code>&lt;html&gt;
  &lt;head&gt;
  &lt;style type="text/css"&gt;
  body{
  margin:0;
  padding:0;
  }
  #header{
  margin:0 auto;
  width:100%;
  background:#efffff;
  height:100px;
  }
  #footer{
  margin:0 auto;
  clear:both;
  width:100%;
  background:#ccc;
  height:100px;
  }
  #wrapper{
  width:990px;
  margin:0 auto;
  background:#000;
  display:block;
  }
  #left{
  margin:0 0 0 15px;
  background:#eeffee;
  width:200px;
  float:left;
  }
  #content{
  margin:0 15px 0 0;
  background:#eeeeee;
  width:760px;
  float:left;
  }
  &lt;/style&gt;
  &lt;/head&gt;
      &lt;body&gt;
          &lt;div id="header"&gt;
              header
          &lt;/div&gt;
          &lt;div id="wrapper"&gt;
              &lt;div id="left"&gt;
                  left
              &lt;/div&gt;
              &lt;div id="content"&gt;
                  content&lt;br/&gt;
                  content&lt;br/&gt;
                  content&lt;br/&gt;
                  content&lt;br/&gt;
                  content&lt;br/&gt;
                  content&lt;br/&gt;
                  content&lt;br/&gt;
                  content&lt;br/&gt;
                  content&lt;br/&gt;
                  content&lt;br/&gt;
                  content&lt;br/&gt;
                  content&lt;br/&gt;
                  content&lt;br/&gt;
                  content&lt;br/&gt;
                  content&lt;br/&gt;
              &lt;/div&gt;
          &lt;/div&gt;
  
          &lt;div id="footer"&gt;
              Footer
          &lt;/div&gt;
      &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>