html5 モバイルアダプティブレイアウトの実装

<style>
   @media only screen and (max-width: 360px) and (min-width: 320px){
    html{
     font-size:13.65px;
    }
   }
   @media only screen and (max-width: 375px) and (min-width: 360px){
    html{
     font-size:23.4375px;
    }
   }
   @media only screen and (max-width: 390px) and (min-width: 375px){
    html{
     font-size:23.4375px;
    }
   }
   @media only screen and (max-width: 414px) and (min-width: 390px){
    html{
     font-size:17.64px;
    }
   }
   @media only screen and (max-width: 640px) and (min-width: 414px){
    html{
     font-size:17.664px;
    }
   }
   @media screen and (min-width: 640px){
    html{
     font-size:27.31px;
    }
   }
  </style>

<script>
   (function(doc, win) {
    var docEl = doc.documentElement, //root element html
     // determine if the window has orientationchange method, if it does, assign to a variable, if not, return to resize method.
     resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',
     recalc = function() {
      var clientWidth = docEl.clientWidth;
      if(!clientWidth) return;
      // Set the document's fontSize to a size that is proportional to the window, thus achieving a responsive effect.
      if(clientWidth >= 640) {
       clientWidth = 640;
      }
      docEl.style.fontSize = 20 * (clientWidth / 320) + 'px';
      console.log(clientWidth);
      console.log(docEl.style.fontSize);
     };
     recalc();
    if(!doc.addEventListener) return;
    win.addEventListener(resizeEvt, recalc, false); //addEventListener event method accepts three parameters: the first is the event name like click event onclick, the second is the function to be executed, the third is a boolean value
    doc.addEventListener('DOMContentLoaded', recalc, false) //bind the browser zoom and load time
   })(document, window);
  </script>

<div id="div2" class="text" style="border: 0.04rem solid #ccc;
            height: 14rem;font-size: 0.5rem;">