Why border of bottom side is not appearing for Asp Menu

I am using Asp Menu in my application In menu item I want to display in border everything is fine but at bottom of this menu items border is not appearing. where i am going wrong

I tried

myborder:last-child {
            border-bottom: 1px solid lightblue;
        }

But No changes where i am going wrong ?

html

<div style="position: absolute; left: 50px; top: 80px;" id="menu">
<asp:Menu AccessKey="N" ID="MainMenu" runat="server" BackColor="Transparent"
BorderColor="Blue" BorderStyle="None" BorderWidth="2px" Font-Names="Arial"
Font-Size="Small" ForeColor="Black" Orientation="Horizontal"
OnMenuItemClick="MainMenu_MenuItemClick" CssClass="myborder"

Style="width: 400px; text-align: left">
<DynamicHoverStyle BackColor="#66ccff" BorderColor="Black" BorderStyle="Solid"
BorderWidth="1px" ForeColor="Black"  />
  <DynamicMenuStyle BackColor="White" BorderColor="Black"
   BorderStyle="Solid" BorderWidth="1px"  />
  <DynamicMenuItemStyle BackColor="White" HorizontalPadding="5px"
   VerticalPadding="2px" CssClass="myborder"/>
       <Items>
           <asp:MenuItem Text="Home" Value="Home"></asp:MenuItem>
           <asp:MenuItem Text="|" Value="|"></asp:MenuItem>
           <asp:MenuItem Text="Master" Value="Master" Selectable="False">
           <asp:MenuItem Text="Assets Master" Value="Assets Master" />
           <asp:MenuItem Text="Staff Master" Value="Staff Master" />
           <asp:MenuItem Text="Group Master" Value="Group Master" />
           <asp:MenuItem Text="Group Cost Center Master" Value="Group Cost Center Master" />
           <asp:MenuItem Text="Cost Center Master" Value="Cost Center Master" />
           <asp:MenuItem Text="Mobile User Login" Value="Mobile User Login" />
      </Items>
    <StaticMenuItemStyle HorizontalPadding="5px"  VerticalPadding="2px" />
    <DynamicSelectedStyle  BackColor="#BFBFBF" />
    <StaticHoverStyle BackColor="#BFBFBF" ForeColor="Black" />
 </asp:Menu>

Screen Shots