Firefox userContent.css code for autocomplete

I would like to style the autocomplete for text input elements. What do I target in my userContent.css to do that? I have tried .autocomplete-richlist, but that seems to apply to the userChrome setting for the address bar. I also tried .textfield-popup which seems to be the class used before XUL. The inspector in Devtools is no use as the autocomplete list disappears as soon as the text box loses focus.