Check checkbox in asp.net

How can I check whether the checkbox is checked or not in ASP.NET?

Default.aspx

<div class="check_all">
 <label class="container">
   Web Design
   <asp:CheckBox ID="CheckBox" runat="server"/>
   <span class="checkmark"></span>
 </label>
 <label class="container">
   Web Development
   <asp:CheckBox ID="CheckBox1" runat="server"/>
   <span class="checkmark"></span>
 </label>
 <label class="container">
   App Design
   <asp:CheckBox ID="CheckBox2" runat="server" />
   <span class="checkmark"></span>
 </label>
</div>