Web-automation.ru

Решение:

Making ASP.NET Buttons Match the default WebSite Template.

<asp:Button ID="Button1" runat="server" Text="Button" CssClass="button"
onmouseover="this.className='buttonhover'"
onmouseout="this.className='button'" />


css:
.button { 
color: White; 
background-color: #465C71;
border:1px solid; 
border-color: Gray; 
} 

.buttonhover { 
color: White; 
background-color: #BFCBD6;
border:1px solid; 
border-color: Gray; 
}