/* media queries which are guaranteed to evaluate to true */
@media all
and ( min-width:
1px),
(max-width: 1000em
) { }
/* media queries which are guaranteed to evaluate to false */
@media all and (max-width: 0px), (min-width: 1000em) { }
@media (min-width: 20px) and (max-width: 10px) { }