<h1>Header 1</h1>
<h2>Header 2</h2>
<h1>Header 1</h1>
<h2>Header 2</h2>

body {
  background: #fedebe;
  counter-reset: headers;
}

h1 {
  counter-increment: headers;
  counter-reset: subheaders;
}

h1:before {
  content: counter(headers) ' - ';
}

h2 {
  counter-increment: subheaders
}

h2:before {
  content: counter(headers) '.' counter(subheaders) ' - ';
}