chromium/third_party/blink/web_tests/fast/css3-text/css3-text-decoration/stable/first-letter-text-decoration.html

<!DOCTYPE html>
<style>
#a::first-letter {
  text-decoration: underline;
}
#b::first-letter {
  text-decoration: green double underline;
}
</style>
<div id="a">The first letter should have an underline in experimental and stable.</div>
<div id="b">The first letter should have a green double underline in experimental only.</div>