chromium/third_party/blink/web_tests/fast/css/first-letter-hover-002.html

<!DOCTYPE html>
<style>
    #t { width: 400px; height: 400px; }
    #t::first-letter { background-color: red; }
    #t:hover::first-letter { background-color: green; }
</style>
<div id="t">
    <div>
        <p>X</p>
        <p>The X above should have a green background when hovered.</p>
    </div>
</div>
<script>
document.body.offsetTop; // Force layout. The mouse is not tracked before first layout.

if (window.eventSender)
    eventSender.mouseMoveTo(100, 100); // Hover.

document.body.offsetTop; // Update layout for the hovered state.
</script>