user/test/com/google/gwt/resources/converter/font-family.css

@def defaultFontFamily Arial,Helvetica,sans-serif;

div {
  font-family: defaultFontFamily;
}

span {
  font-family: Helvetica, Comic sans MS, defaultFontFamily;
}

.someClass {
  font-family: Arial Unicode MS, Arial, sans-serif !important;
}