@media screen and (max-width:503px) {
 
 main {
   margin-top:5em;
 }

}

@media screen and (min-width: 504px) and (max-width:768px) {
 
 main {
   margin-top:6em;
 }

}
@media screen and (min-width: 768px) {
 
    main {
      margin-top:9em;
    }
  
}