SOURCE

document.addEventListener('DOMContentLoaded', function(e) {
  	 // 设置rem值
            const el = document.querySelector('html')
            console.log('el', el, el.style)
            el.style.fontSize = `${window.innerWidth / 10}px`
}, false);

<div class="box1"></div>

@function px2rem($px){
    $rem : 75px; // '750/10':分成10份
    @return ($px/$rem) + rem;
}

// foo.scss

.box1 {
 	width: px2rem(320px); // '(320/750) * 10 = 4.266rem'
  height: 100px;
  background: red;
 }