@media screen and (min-width: 320px) {
  html {
    font-size: 32px;
  }
}
@media screen and (min-width: 375px) {
  html {
    font-size: 37.5px;
  }
}
@media screen and (min-width: 414px) {
  html {
    font-size: 41.4px;
  }
}
@media screen and (min-width: 750px) {
  html {
    font-size: 75px;
  }
}

<script>
  // 根据屏幕尺寸大小调整html的fontsize
  function setHtmlFontSize() {
    const width = document.documentElement.clientWidth;
    document.documentElement.style.fontSize = width / 10 + "px";
  }
  //   初始化
  setHtmlFontSize();
  //   监听屏幕尺寸变化事件
  window.addEventListener("resize", setHtmlFontSize);
  //   监听屏幕翻转事件
  window.addEventListener("orientationchange", setHtmlFontSize);
</script>

//定义设计稿宽度为375
const DESIGN_WIDTH = 375;
//通过设置meta元素中content的initial-scale值达到移动端适配
const setViewport = function () {
  //计算当前屏幕的宽度与设计稿比例
  let scale = window.screen.width / DESIGN_WIDTH;
  // 获取元素
  let meta = document.querySelector("meta[name=viewport]");
  let content = `width=${DESIGN_WIDTH}, initial-scale=${scale}, maximum-scale=${scale}, minimum-scale=${scale}`;
  // 判断是否已存在
  if (!meta) {
    meta = document.createElement("meta");
    meta.setAttribute("name", "viewport");
    document.head.appendChild(meta);
  }
  meta.setAttribute("content", content);
};
setViewport();
//   监听屏幕变化事件
window.addEventListener("resize", setViewport);
//   监听屏幕翻转事件
window.addEventListener("orientationchange", setViewport);