https://www.reddit.com/r/emacs/comments/fcernd/how_to_find_the_highlight_face_in_emacs/

The doom themes I try all have too un-obvious a background color for selected text – the text of future matches when doing an interactive search, or the highlight color of matches while I’m spell-checking, or the mark area when I am highlighting a section of text. I assume these are all the same face, because they look the same. Does anyone know which face this should be so I can customize it, and secondly, can tell me how I could figure out the answer to this question on my own without reading a lot of code?

Answer: (list-faces-display)

The actual faces for me were lazy-highlight.