UserAgent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.92 Safari/537.36

Steps to reproduce the problem:
1. Use the built-in GTK+ theme (Settings > Themes > Use GTK+)
2. Click the gear-shaped icon on the bottom left corner on a new tab to customize it

What is the expected behavior?
Chromium should allow me to change the new tab page's background and show buttons to change it

What went wrong?
There is only one option available: "Restore default shortcuts", as if I was using a custom theme

Did this work before? N/A 

Chrome version: 69.0.3497.92  Channel: stable
OS Version: 4.18.6-1-MANJARO
Flash Version: