hover effect on asp:hyperlink control without navigate url property

I have a hyperlink control which I am opening a popup.

<asp:HyperLink ID="hlnk" runat="server" Text="About" Target="_blank" />

I am setting the onclick attribute from code behind

string basePath = this.ResolveClientUrl("~/Pages/About.aspx");
hlnk.Attributes.Add("onclick", @"javascript:w= window.open('" + basePath + "','mywin','left=20,top=20,width=460,height=200,toolbar=0,resizable=0');");


Now problem is that hover effect is now not coming.Please let me know how to let it hover

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