移动端字体自适应

@media screen and (min-width:321px) and (max-width:375px){html{font-size:10px}}

@media screen and (min-width:376px) and (max-width:414px){html{font-size:10px}}

@media screen and (min-width:415px) and (max-width:639px){html{font-size:12px}}

@media screen and (min-width:640px) and (max-width:719px){html{font-size:12px}}

@media screen and (min-width:720px){html{font-size:16px}}

@media screen and (min-width:750px) and (max-width:799px){html{font-size:23.5px}}

@media screen and (min-width:800px)and (max-width:1199px){html{font-size:25px}}

@media screen and (min-width:1200px){html{font-size:30px}}

div.box{

font-size: 2rem;

height: 10rem;

background: black;

color: white;

padding: 1rem;

}