I'm looking for something like this except with a white background and no border.
Note that I have no Lua experience so if you can please don't use it :)
:)
\colorbox{}{}
\colorbox{green!20}{l a b}
\colorbox{}{}does that: try\colorbox{green!20}{l a b}as a test. The linked question is about displaying the bounding boxes of glyphs. – Cicada May 05 '20 at 08:52