Your system information

• Steam client version (build number or date):
  Built: Nov 29 2017 at 14:05:08
  Steam API: v017
  Steam package versions: 1512000021
• Distribution (e.g. Ubuntu): Linux Mint 18.2 Sonya (64 bit) (Ubuntu Distro)
• Opted into Steam client beta?: [Yes/No] Yes (Bug also appears in the stable version.)
• Have you checked for system updates?: [Yes/No] Yes

Please describe your issue in as much detail as possible:

Attempting to load a review video from the steam page will cause the resolution to display incorrectly. This also happens while watching steam broadcasts. A better example is the following image down below.

I expected the fullscreen window to consume the entire screen space. And not just a fraction of it.

Steps for reproducing this issue:

1. Click on any store page or watch a steam broadcast.
2. Enter fullscreen mode on a video.