头部必写<meta name="viewport" content="width=device-width,initial-scale=1,maximum-scale=1,user-scalable=no">@media screen and (min-width:0px) and (max-width: 480px) {body{background: #797;}div{width: 48%}}@media screen and (min-width:481px) and (max-width: 1024px) {body{background: #aaa;}div{width: 31.3333%}}@media screen and (min-width:1025px) and (max-width: 1200px) {body{background: #8cc;}div{width: 23%}}@media screen and (min-width:1201px) and (max-width: 1920px) {body{background: #999;}div{width: 23%}section{width: 1200px;margin:auto;}}