媒体查询

html{
   font-size:10px
}
@media screen and (min-width:321px) and (max-width:375px){
   html{
       font-size:11px
   }  
}
@media screen and (min-width:376px) and (max-width:414px){
   html{
       font-size:12px
   }
}
@media screen and (min-width:415px) and (max-width:639px){
   html{
       font-size:15px
   }
}
@media screen and (min-width:640px) and (max-width:719px){
   html{
       font-size:20px
   }
}
@media screen and (min-width:720px) and (max-width:749px){
   html{
       font-size:22.5px
   }
}
@media screen and (min-width:750px) and (max-width:799px){
   html{
       font-size:23.5px
   }
}
@media screen and (min-width:800px){
   html{
       font-size:25px
   }
}