title: XHTML CSS background not filling entire div
body: <p>I've got a page that has a background color for the main container, but for some reason, the color ends just below the header div. The page and the CSS validate in the w3 validators, though, and I have no idea why and I've tried several different fixes.</p>
  
  <p>CSS</p>
  
  <pre><code>body{
      margin:0;
      padding:0;
      line-height: 1.5em;
      background-color: #e5e5dc;
      color: #000;
  }
  
  #maincontainer{
      background-color: green;
      width: 98%;
      margin: 0 auto;
      border: 1px solid black;
  }
  
  #topsection{
      background-color: transparent;
      height: 90px; /*Height of top section*/
  }
  
  #logo{
      background-image: url();
      text-align: center;
      margin: 0 auto;
      width: 100%;
  }
  
  #contentwrapper{
      float: left;
      width: 100%;
      background-color: transparent;
  }
  
  #contentcolumn{
      margin-right: 230px; /*Set right margin to RightColumnWidth*/
  }
  
  #rightcolumn{
      float: left;
      width: 230px; /*Width of right column in pixels*/
      margin-left: -230px; /*Set left margin to -(RightColumnWidth) */
      background-color: transparent;
  }
  
  #footer{
      clear: left;
      width: 100%;
      background-color: transparent;
      text-align: center;
      padding: 4px 0;
      border-top: 1px solid black;
  }
  
  .innertube{
      margin: 10px; /*Margins for inner DIV inside each column (to provide padding)*/
      margin-top: 0;
  }
  
  .error{
      background-image: url("images/misc/scroll.jpg");
      background-position: top left;
      background-repeat: no-repeat;
  }
  
  a:link, a:visited{
      color: #000;
      text-decoration: none;
  }
  
  a:hover, a:active{
      color: #000;
      text-decoration: underline;
  }
  </code></pre>
  
  <p>EDIT -- Raw html source straight from view source in my browser</p>
  
  <pre><code>&lt;!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
  "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"&gt; 
  &lt;html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"&gt; 
  &lt;head&gt; 
      &lt;meta http-equiv="Content-Type" content="text/html; charset=utf-8" /&gt; 
      &lt;title&gt;Haven &amp;bull; Login&lt;/title&gt; 
      &lt;link href="includes/style.css" rel="stylesheet" type="text/css" /&gt; 
  
  
      &lt;script src="includes/jquery.js" type="text/javascript"&gt;&lt;/script&gt; 
      &lt;script type="text/javascript"&gt; 
  
      function init()
      {
          var e = document.createElement('script');
          e.src = 'includes/all.js';
          document.getElementById('script_insertion').appendChild(e);
      }
      &lt;/script&gt; 
  &lt;/head&gt; 
  &lt;body onload="init();"&gt; 
  &lt;div id="script_insertion"&gt;&lt;/div&gt; 
  &lt;div id="maincontainer"&gt; 
      &lt;div id="topsection"&gt; 
          &lt;div class="innertube"&gt; 
              &lt;h1&gt;IMG&lt;/h1&gt; 
          &lt;/div&gt; 
      &lt;/div&gt; 
  
      &lt;div id="contentwrapper"&gt; 
          &lt;div id="contentcolumn"&gt; 
              &lt;div class="innertube"&gt; 
                  &lt;form action="./login.php?mode=login" method="post"&gt; 
                      &lt;table&gt; 
                          &lt;tr&gt; 
                              &lt;td&gt;Username:&lt;/td&gt; 
                              &lt;td&gt;&lt;input type="text" name="username" id="username" size="10" title="Username" /&gt;&lt;/td&gt; 
                          &lt;/tr&gt; 
                          &lt;tr&gt; 
                              &lt;td&gt;Password:&lt;/td&gt; 
                              &lt;td&gt;&lt;input type="password" name="password" id="password" size="10" title="Password" /&gt;&lt;/td&gt; 
                          &lt;/tr&gt; 
                          &lt;tr&gt; 
                              &lt;td&gt;&lt;input type="reset" value="Clear" /&gt;&lt;/td&gt; 
                              &lt;td&gt;&lt;input type="submit" name="login" value="Login" /&gt;&lt;/td&gt; 
                          &lt;/tr&gt; 
                      &lt;/table&gt; 
                      &lt;input type="hidden" name="remember" value="true" /&gt; 
                  &lt;/form&gt; 
                  &lt;br /&gt; 
                  Don't have an account yet? &lt;a href="./register.php"&gt;Register here!&lt;/a&gt; 
              &lt;/div&gt; 
          &lt;/div&gt; 
      &lt;/div&gt;  &lt;div id="rightcolumn"&gt; 
          &lt;div class="innertube"&gt; 
              Chat
          &lt;/div&gt; 
      &lt;/div&gt; 
  &lt;/div&gt; 
  &lt;/body&gt; 
  &lt;/html&gt;
  </code></pre>