Well, the problem is that visual studio always tries to check for css 1.0 when I open any file, and I need to reset it to 2.1 every time I open any css file.so they asked if there is a way to set the default value to 2.1? thanks
I found the answer at http://forums.asp.net/t/1486063.aspx/1well, it seems that to change the default CSS check, you need to change the default default html check from "Tools"> "Options"> "Text Editor"> "HTML"> "Check".so I changed the target to XHTML 1.0 Transitional, and now css is checked to 2.1 by default :)