changing selected menu item style

Trying to set the selected menu item style, but it's not working.  Have the following menu...
        <asp:Menu ID="NavigationMenu" runat="server" EnableViewState="false" IncludeStyleBlock="false"
            Orientation="Vertical" StaticDisplayLevels="1" >
            <StaticSelectedStyle CssClass="menuSelected" />
            <Items>
                <asp:MenuItem NavigateUrl ="~/page1.aspx" Text="Page 1" />
                <asp:MenuItem NavigateUrl ="~/page2.aspx" Text="Page 2" />
            </Items>
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