first-letter-to-non-block-container.html

<!DOCTYPE html>
<style>
.first-letter::first-letter {
  color: red;
}
.flex {
  display: flex;
}
</style>
<p>Tests pass if initial "R" are in red and "X" are in black.</p>
<div class="first-letter">R first-letter applies in div.</div>
<div class="first-letter flex">X first-letter do not apply if display: flex</div>
<fieldset class="first-letter flex">X first-letter do not apply if display: flex, even in fieldset</fieldset>

chromium/third_party/blink/web_tests/fast/css/first-letter-to-non-block-container.html