It seems like any version newer than 70.0.3538.110 for www-client/google-chrome (the current version being 71.0.3578.80) has a broken dark mode where the GTK theme is no longer honored and the omnibar is white instead of dark.
It also breaks the workaround using the chrome://flags/#top-chrome-md flag set to "Normal". Just found an upstream bug as well: https://bugs.chromium.org/p/chromium/issues/detail?id=863230
Nothing I can do about this.
No contacts within the chrome device team?