Edit in JSFiddle

<div class="demo demo12">
  <h2>毎朝ちゃんと飲むUX</h2>
  <h2>毎朝ちゃんと飲むUX</h2>
  <h2>毎朝ちゃんと飲むUX</h2>
</div>

.demo {
  width: 500px;
  margin: 0 auto;
  padding: 10px 0;
  font-family: sans-serif;
  font-size: 20px;
  color:#3cb3e4;
}
.heading {
  margin: 10px 0
}
.demo {
  counter-reset: h2;
}
.demo12 h2:before {
  content : counter(h2,decimal) ". ";
  counter-increment : h2;
}