index.html

<!DOCTYPE html>
<html>

<head>
  <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, minimum-scale=1, user-scalable=no">

  <meta charset="utf-8">
  <title>stone</title>
  <script>
  (function() {
    var baseFontSize = 100;
    var baseWidth = 375;

    var set = function() {
      var clientWidth = document.documentElement.clientWidth || window.innerWidth;

      var rem = 100;
      if (clientWidth != baseWidth) {
        rem = Math.floor(clientWidth / baseWidth * baseFontSize);
      }

      document.querySelector('html').style.fontSize = rem + 'px';
    }
    set();

    window.addEventListener('resize', set);
  }());
  </script>
</head>

<body>
  <div id="app"></div>
  <!-- built files will be auto injected -->
</body>

</html>