750px 等于 7.5rem

<script>

!function (n) {

    var e = n.document,

    t = e.documentElement,

    i = 750,

    d = i / 100,

    o = "orientationchange" in n ? "orientationchange" : "resize",

    a = function () {

        var n = t.clientWidth || 320;

        n > 750 && (n = 750);

        t.style.fontSize = n / d + "px"

    };

    e.addEventListener && (n.addEventListener(o, a, !1), e.addEventListener("DOMContentLoaded", a, !1))

}(window);

</script>
<style>

* {

margin: 0;

padding: 0;

list-style: none;

text-decoration: none;

}

 

.fl {

float: left;

}

 

.fr {

float: right;

}

 

.pr {

position: relative;

}

 

.clear {

clear: both;

}

 

.cf {

zoom: 1;

}

 

.cf::after {

display: block;

height: 0;

clear: both;

font-size: 0;

content: '.';

visibility: hidden;

}

</style>