Chrome Version: 71.0.3543.0
OS: ChromeOS

What steps will reproduce the problem?
(1) Launch the browser on ChromeOS.
(2) Install a theme with a fairly light frame background (such as 'Into The Mist': https://chrome.google.com/webstore/detail/into-the-mist/mgihmkgobaljfehcadcckdggpeojaadh?hl=en-US).

What is the expected result?
The caption buttons (close, minimize, etc) should be clearly visible .

What happens instead?
The caption buttons can be difficult to make out, as they are drawing as a light grey on top of a background that is various shades of white and black.