<p>フォントサイズ100%</p>
<div>
  フォントサイズ200%
  <p>フォントサイズ50%</p>
</div>
* {
  background-color: #3b3f47;
  color: #fff;
  font-family:"游ゴシック", "YuGothic", "Yu Gothic", 'ヒラギノ角ゴ ProN W3', "Hiragino Kaku Gothic ProN", "Meiryo", Helvetica, Arial, sans-serif;
  text-align: center;
}

p {
  font-size: 100%;  /*16px*/
}   

div {
  font-size: 200%;  /*32px*/
}   

div p {
  font-size: 50%;  /*16px*/
}   

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