@media screen and (min-width:768px) and (max-width:959px) {

}

@media screen and (max-width:639px) {
/*　640pxはここを読み込む　*/
}

@media screen and (max-width:480px) {
/*　480pxはここを読み込む　*/
}

@media screen and (max-width:320px) {
/*　320pxはここを読み込む　*/
}