Canceling switch to light mode stays in light mode

[waltman]

Describe the bug
I opened CaPTk and looked in Preferences. I switched to light mode. I clicked Cancel, but it stayed in light mode. This seems to only happen when I first start CaPTk, and after that it's OK.

To Reproduce
Steps to reproduce the behavior:

1. Start running CaPTk
2. Go to File/Preferences
3. Change theme from Dark to Light
4. Click OK
5. Click Cancel
6. The UI stays in Light Mode

Expected behavior
The UI should revert to Dark Mode when the Cancel button is clicked.

Screenshots
If applicable, add screenshots to help explain your problem.

CaPTk Version
v.1.9.0.Alpha

Desktop (please complete the following information):

• Ubuntu 20.04.3 LTS
• macOS Monterey 12.1