title: CSS properties not available
body: <p>I am using MS expression 4 for building this website and when I try to set some properties they are not available. The two I have come across so far are border-radius and background-size. I am sure I will come across more but I was wondering why that is and how I can get them so I can use them. the error says "the property is marked invalid because it is not covered by the current schema"</p>
  
  <p>Thank you</p>