JavaScript 1 rem

window.onload = function () {
    setRem(750, 100);
};

window.onresize = function () {
    setRem(750, 100);
};

function setRem(designWidth, designRem) {
    let html = document.getElementsByTagName("html")[0];
    let clientWidth = document.body.clientWidth || document.documentElement.clientWidth;
    html.style.fontSize = designRem * clientWidth / designWidth + "px";
}

750的设计稿，根据屏幕实际大小按比例缩放 fontSize.