Edit in JSFiddle

<section id="sec01">
  <p>フォントとサイズが反映されない</p>
  <label for="name">Name</label>
  <input id="name" type="text" placeholder="firstname lastname">
  <textarea>textarea</textarea>
  <select>
    <option>select01</option>
    <option>select02</option>
    <option>select03</option>
  </select>
  <button>Button</button>
</section>

<section id="sec02">
  <p>フォントとサイズが反映される</p>
  <label for="name">Name</label>
  <input id="name" type="text" placeholder="firstname lastname">
  <textarea>textarea</textarea>
  <select>
    <option>select01</option>
    <option>select02</option>
    <option>select03</option>
  </select>
  <button>Button</button>
</section>

@import url("https://fonts.googleapis.com/css?family=Rokkitt");

html {
  font-size: 30px;
}
section {
  border: 1px solid black;
  margin: 10px;
  padding: 10px;
}

#sec01 {
  font-family: "Rokkitt";
  
  > * {
    display: block;
    margin: 10px 0;
  }
}
#sec02 {
  font-family: "Rokkitt";
  > input, textarea, select, button {
    font-family: inherit;
    font-size: 100%;
  }

  > * {
    display: block;
    margin: 10px 0;
  }
}