.outside{    width: 500px;    height: 300px;}/*写一个色块，x>1000黄色，800<x<1000绿色，500<x<800红色，x<500灰色*/@media screen and (max-width: 500px){    .outside{        background: gray;    }}@media screen and (min-width: 500px) and (max-width: 800px){    .outside{        background: red;    }}@media screen and (min-width: 800px) and (max-width: 1000px){    .outside{        background: green;    }}@media screen and (min-width: 1000px){    .outside{        background: yellow;    }}