Interface transparency looks to be broken on Mac OS.

[ben-ryder]

Describe the bug
When viewing the game on mac OS the interface transparency is not working.
It appears to still be working fine in the menus, it's just within the game itself.

To Reproduce
Steps to reproduce the behaviour:

1. Start playing the game and you will see the interface doesn't have transperency.

Expected behaviour
Interface backgrounds should have transprency.

System Information (please complete the following information):

• OS: Mac (Big sur)
• Conqueror of Empires Version: all versions. Tested on master & develop branch.
• Python Version: Python 3.6.7
• Pygame Version: 2.0.1

Additional context
I originally built the game with pygame 1.9.x so it's possible something around transparency has changed in pygame 2.x

[ben-ryder]

It looks like there might be a few more transparency issues than I thought: