$tablet_upper: 1024px;
$phone_upper: 603px;
 
@mixin phone {
  @media (max-width: $phone_upper) {
    @content;
  }
 
} // @mixin phone
 
@mixin tablet {
 
  @media (min-width: $phone_upper+1) and (max-width: $tablet_upper) {
    @content;
  }
 
} // @mixin tablet