@import url("osstyle_pc.css");  

@media screen and (min-width: 0px) and (max-device-width: 320px) {
         @import url("osstyle_phone.css");  
}
@media screen and (min-width: 321px) and (max-device-width: 920px) {
         @import url("osstyle_tab.css");  
}
@media screen and (min-width: 911px)  {
         @import url("osstyle_pc.css");  
}