Focus Mode window has a very large titlebar

Issue:
When a tab is in focus mode, the resulting window has a massive titlebar with lots of blank space. In chrome the titlebar is very slim and contains only the title and the control buttons.

To reproduce:

  1. chrome://flags/
  2. Enable “Focus Mode” and relaunch the browser
  3. Right click on any tab > Focus mode

Please see screenshots for comparison.

Brave version:
Stable 1.0.1
Beta and Nightly are also affected.

NOTE: I have tested this only on Debian however it may affect all OSs.