<div>
<h2>皮卡丘</h2>
  <div>
    <h3>皮丘</h3>
    <h3>皮卡丘</h3>
  </div>
<h2>小火龍</h2>
  <div>
    <h3>小火龍</h3>
    <h3>火恐龍</h3>
  </div>
<h2>妙蛙種子</h2>
</div>
div{
  counter-reset:num 1 section;
}
h2::before {
  counter-increment:num; 
  content:counter(num) '. ';
}
h3::before {
  counter-increment:section; 
  content:counter(section, lower-roman) '. ';
}

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