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">  

```