*{margin: 0;padding: 0;font-family: "Microsoft YaHei", simsun, Arial, sans-serif, Mingliu, Verdana, Helvetica, Lucida;}
html{font-size:20px;}
div{background: #f00;color: #fff;text-align: center;padding:15px 0;}
p{text-align: center;padding:15px 0;background:#ccc;}
p:after{content: '@media：750及以上';;}
@media screen and (max-width: 750px) {
  html{font-size:20px;}
  p:after{content: '@media：640-750区间';}	
}
@media screen and (max-width: 640px) {
  html{font-size:18px;}
  p:after{content: '@media：414-640区间';}	
}
@media screen and (max-width: 414px) {
  html{font-size:16px;}
  p:after{content: '@media：375-414区间';}	
}
@media screen and (max-width: 375px) {
  html{font-size:14px;}
  p:after{content: '@media：320-375区间';}	
}
@media screen and (max-width: 320px) {
  html{font-size:12px;}
  p:after{content: '@media：320及以下';}	
}