// 手机端自动判断 rem
<script type="text/javascript">
(function() {var b = document.documentElement,
a = function() {var a = b.getBoundingClientRect().width;
var a = a < 640 ? a : 640;
b.style.fontSize =( .0375 * a) + "px";
},
c = null;
window.addEventListener("resize",
function() {
clearTimeout(c);
c = setTimeout(a, 300);
});
a();
})();
</script>