For \<button> and \<input>: add an offset to the current focus outline and effect a change in the background color of the button to increase visibility. It may be useful to add offset in other areas as well to ensure the outline doesn't obstruct whatever it's highlighting.
For \<li> with role = option: add a bottom border to current background change on focus so indication is not by color alone.
Tagging in @jkva for this.
Thanks go to Lauren for these two sugestions.