css – 如何组合两个媒体查询？

@media only screen 
and (min-device-width : 320pX) 
and (max-device-width : 480pX) 
and (orientation : landscapE){
#div {margin-top: 20px;}
}

}
@media only screen 
and (min-device-width : 481pX) 
and (max-device-width : 1024pX) 
and (orientation : porTrait){
{margin-top: 20px;}
}