避免在ASP中出现“未定义类或CssClass值”警告。NET MVC ASCX部分视图(用户控件)

I wondered how I can stop those annoying compiler warnings "The class or CssClass value is not defined" coming from my ASP.NET MVC partial views/ASCX user controls. The CSS is correctly defined, but the reference to the CSS file is obviously on the master page only. My partial views contain lots of CSS class references on div's etc. and so I get massive amounts of warnings which I shouldn't see. I wondered how I can stop those annoying compil