title: ajax dropdown extender at runtime
body: <p>I've got a textbox with an ajax dropdown extender. How do I make it look like image 2 at runtime and not only when hovering over the textbox. 
  The textbox with the "downbutton" should look like image 2 at design time</p>
  
  <p><img src="https://i.stack.imgur.com/1FzEf.png" alt="Image 2 to look like at runtime"></p>
  
  <p>How do I do this or some good reading material on how to do this?</p>
  
  <p>EDIT</p>
  
  <p>All I've done is this so far as I'm trying to first display it correctly, otherwise i will have to find another way:</p>
  
  <pre><code>    &lt;asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent"&gt;
  &lt;asp:ScriptManager ID="ScriptManager1" runat="server"&gt;
              &lt;/asp:ScriptManager&gt;
      &lt;div&gt;
  
         &lt;asp:TextBox ID="txtResidence" runat="server"&gt;&lt;/asp:TextBox&gt;
         &lt;asp:DropDownExtender ID="txtResidence_DropDownExtender" runat="server" 
             DynamicServicePath="" Enabled="True" TargetControlID="txtResidence"
             DropDownControlID="pnlRes"&gt;
         &lt;/asp:DropDownExtender&gt;
  
     &lt;/div&gt;
     &lt;div&gt;
           &lt;asp:Panel ID="pnlRes" runat="server"&gt;
          &lt;asp:TreeView ID="ResidenceTreeView" runat="server" ShowLines="true" PopulateNodesFromClient="false" BackColor="#99CCFF" style="width:100%" ShowExpandCollapse="false"&gt;
              &lt;Nodes&gt;
                  &lt;asp:TreeNode Text="1" Value="1"&gt;
                      &lt;asp:TreeNode Text="1.1" Value="1.1"&gt;&lt;/asp:TreeNode&gt;
                      &lt;asp:TreeNode Text="1.2" Value="1.2"&gt;&lt;/asp:TreeNode&gt;
                  &lt;/asp:TreeNode&gt;
                  &lt;asp:TreeNode Text="2" Value="2"&gt;
                      &lt;asp:TreeNode Text="2.1" Value="2.1"&gt;&lt;/asp:TreeNode&gt;
                      &lt;asp:TreeNode Text="2.2" Value="2.2"&gt;&lt;/asp:TreeNode&gt;
                  &lt;/asp:TreeNode&gt;
              &lt;/Nodes&gt;
          &lt;/asp:TreeView&gt;
          &lt;/asp:Panel&gt;
     &lt;/div&gt;
  &lt;/asp:Content&gt;
  </code></pre>