Polyfill for ruby-position:under; Hackishly displays the <rt> tag underneath the <ruby> tag.

ruby-position-under-polyfill.css

/*
* browser support: Webkit, Gecko, MS browsers [ALL OK]
* sauce: https://twitter.com/SethC1995/status/1279827154788913152 (extra info in self-replies)
*/

/* text-align, font-size, margin, bottom, line-/height may all be adjusted to fit preferences */
ruby {
  text-align:center;
  display:inline-block;
  position:relative;
  bottom:-16px;
  margin:-16px 0 16px 0;
}

ruby rt {
  font-size:11px;
  display:block;
  height:15px;
  line-height:15px;
  margin-top:-1px; /*optional; keeps furigana closer to origin */
}