title: trouble overlapping divs in asp.net using float
body: <p>aspx:</p>
  
  <pre><code>&lt;div id="home_tabs" CssClass="home_tabs" runat="server"&gt;
                      &lt;asp:Button ClientIDMode="static" Text="Cures" 
                          ID="cures_btn" CssClass="home_tab" runat="server" onclick="cures_btn_Click" /&gt;
                      &lt;div id="home_tabs_line" CssClass="home_tabs_line" runat="server"&gt;&lt;/div&gt;
                  &lt;/div&gt;
  </code></pre>
  
  <p>css:</p>
  
  <pre><code>.home_tab 
  {
      vertical-align: top !important;
      height: 46px;
      padding: 0px 15px !important;
      line-height: 46px !important;
      background: #cecece !important;
      border-radius: 0px !important;
      box-shadow: none !important;   
      color: #000 !important;
      border: solid #fff 1px !important;
      border-bottom-width: 0px !important;
      margin-right: 10px !important;
      padding-left: 50px !important;
      z-index: 10;
  }
  
  .home_tabs_line 
  {
      float: left;
      width: 100%;
      vertical-align: middle;
      height: 1px;
      z-index: 0;
      margin-bottom: 10px;
  }
  
  .home_tabs {
     height: 46px;
  }
  </code></pre>
  
  <p>I would like the home_tabs_line to go under the home_tab div. I gave them z-indexes and floated the line left. Why are they not overlapping?</p>