Stying and CSS in ASP.Net

private void Page_Load(object sender, System.EventArgs e)
{
	if(IsPostBack)
	{	
		Style Sty=new Style();
		Sty.BackColor=Color.Yellow;
		Label1.ApplyStyle(Sty);
	}
}

.buttonstyle { BACKGROUND-COLOR: lightblue }

asp:button id="Button1" runat="server" Text="Click" CssClass="buttonstyle"

asp:button id="Button1" runat="server" Text="Click" Class="buttonstyle"