HTML/CSS自动编号标题？

body {
  counter-reset: section;
}

h1:before {
  counter-increment: section;
  content: counter(section) ". ";
}

<h1>标题1</h1>
<h1>标题2</h1>
<h1>标题3</h1>

1. 标题1
2. 标题2
3. 标题3

body {
  counter-reset: section;
}

h1:before {
  counter-increment: section;
  content: counter(section) ". ";
}

h2:before {
  counter-increment: subsection;
  content: counter(section) "." counter(subsection) " ";
}

<h1>标题1</h1>
<h2>子标题1.1</h2>
<h2>子标题1.2</h2>
<h1>标题2</h1>
<h2>子标题2.1</h2>

1. 标题1
1.1 子标题1.1
1.2 子标题1.2
2. 标题2
2.1 子标题2.1