I think he is talking about the bookmarks dropdown turning black because of the stupid new Dark Mode.
I hate the Dark Mode. It is another dumb thing from the idiots at Google.

Down at the bottom of your screen. They call it your Shelf. I call it your Task Bar.
Right click that, and click Set Wallpaper.
There you will see the settings for Dark Moded and Light Mode.
That in English means changing your white pages black.