[Android 11] Settings Light/Dark theme application "confusing"

[AlbinoGeek]

Describe the bug:

It seems the Settings dialog can get very "confused" applying a theme:

• Theme does not apply outside of settings dialog until force quit of app
• Theme apply leaves settings dialog "grey" (half-applied?) until re-opened

To Reproduce:

Steps to reproduce the behaviour:

1. Run fyne demo from appstore
2. Go to Hamburger -> File -> Settings
3. Change the Theme
4. Notice that the Settings window is now half-applied (grey)
5. Notice that all other demos theme does not change
6. Force quit fyne demo
7. Run fyne demo, theme is correctly applied now.

Screenshots:

Peek.2021-03-03.11-29.mp4

Device (please complete the following information):

• OS: Android 11 - Samsung Galaxy S20+ Ultra 5G
• Go version: N/A
• Fyne version: v2.0.0 ?

[andydotxyz]

Removed the settings on mobile - they can reappear once we have found a way to support global settings on mobile devices (probably just Android).