I have a div element:
<div class="tab-pane active" id="portlet_tab1">
I want to control this element from the code-behind page and remove the class "active"
NOTE:
- Div doesn't contain the - runat="server"property.
- This is not the master page file but this is another file named "AssignImages.aspx" and it contains ContentPlaceHolder. 
The div is inside this ContentPlaceHolder:
<asp:Content ContentPlaceHolderID="ContentPlaceHolder1" runat="server" ID="Content1">  
 
     
     
     
     
     
     
     
     
    