Responsive style media query in stylesheet

/**********************************//***************iPhone Landscape*************/
@media only screen and (max-width: 767px) and (min-width: 480px){
}
/***************iPhone Portrait**************/
@media only screen and (max-width: 479px) and (min-width: 320px){
}
/**************iPad Landscape***************/
@media only screen and ( max-width: 1024px ) and (min-width: 986px){
}
/********************************************//**************iPad Portrait***************/
@media only screen and (max-width: 985px) and (min-width: 768px){
}