怎么设置（控制）移动端的字体大小

html {font-size:12px}
@media screen and (min-width:480px) 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) and (max-width:959px) {html {font-size: 25px;}}
@media screen and (min-width:960px) and (max-width:1079px) {html {font-size: 30px;}}
@media screen and (min-width:1080px) {html {font-size: 32px;}}

document.getElementsByTagName(‘html‘)[0].style.fontSize = Math.min(window.innerWidth*12/320,40)+"px";