I'm seeing the problem in xorg sessions too. Note that VLC’s user interface is a Qt application. Chromium is a snap, and not a pure GTK application (although using GTK to draw window decorations and menus), as pointed out by Daniel. Similarly, firefox is not a pure GTK application.
Also of interest: gnome-terminal (a pure GTK application) doesn't respect any theme setting, its window title bar is always dark.
I'm seeing the problem in xorg sessions too. Note that VLC’s user interface is a Qt application. Chromium is a snap, and not a pure GTK application (although using GTK to draw window decorations and menus), as pointed out by Daniel. Similarly, firefox is not a pure GTK application.
Also of interest: gnome-terminal (a pure GTK application) doesn't respect any theme setting, its window title bar is always dark.