Test

<html><body><section><div><figure> <html::first-letter style="font-size: 24 pt; float: left;"> <section::first-letter style="color: red; float: left;"> <div::first-letter style=""> T</div::first-letter></section::first-letter></html::first-letter> est</figure></div></section></body></html>

window.getComputedStyle(<html>, '::first-letter') has
window.getComputedStyle(<body>, '::first-letter') has
window.getComputedStyle(<section>, '::first-letter') has
window.getComputedStyle(<div>, '::first-letter') has
window.getComputedStyle(<figure>, '::first-letter') has