Theme and UI enhancements

[Brottweiler]

Hi, I hope this is okay that I am making one issue with some enhancement requests. If not, I'll make several. Also thanks for this app, I like and prefer how it's open source and updated compared to other apps.

Enchancement requests

Theme

• "Use system default" theme should be default. Right now, light theme is default even if phone has dark theme enabled.
• There should be an option for even darker dark theme. The current dark theme is gray. A completely black dark theme would be nice to have on OLED phones.

User Interface

• Add an option to fullscreen the app, hiding the top and botton bar (if any), and also make it so you only see the number on a black background. This would save battery on phones with OLED screens and look pretty slick. You still just tap the number to count up.
• Add a hold to reset, instead of having to press the three dots, then "delete counter".

[amarradi]

I have the Same issue. I have changed my android system to the dark look. In the app, I have set the system settings to load. Unfortunately, the app remains light and does not go dark