button-first-line-first-letter.html

<!DOCTYPE html>
<style>
  .line::first-line { color: red }
  .letter::first-letter { color: green; }
</style>

<button class=line>
  First line should be red<br>
  This is the second line.
</button>

<button class=letter>
  First letter should be green<br>
  This is the second line.
</button>

chromium/third_party/blink/web_tests/fast/forms/button/button-first-line-first-letter.html