get HTML Elements using MasterPage and C#

I have a short script like below. This is a webpage inherited from a MasterPage. Now, I want to check wheter checkbox cmn-toggle-1 is checked in code behind using C#. How can I make it?

<asp:Content ID="Content1" ContentPlaceHolderID="HeadContent" runat="server">
  <link rel="stylesheet" type="text/css" href="Styles/slide_button_style.css">
  <link rel="stylesheet" type="text/css" href="Styles/ajax-accordition.css">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="FeaturedContent" runat="server">
  <asp:Label ID="Label_Status" runat="server"></asp:Label>
</asp:Content>
<asp:Content ID="Content3" ContentPlaceHolderID="MainContent" runat="server">
  <input id="cmn-toggle-1" type="checkbox">
</asp:Content>