Github Night Theme Makes Images With Transparent Background Illegible

[ghost]

Hi there, I was just checking out this repository for the first time and noticed your flow chart of system architecture has arrows that end up being hidden if you're viewing github using "night theme".

[ghost]

I have little image editing experience - but I create a pull request with the image updated from transparent to white background here:
#781

[ghost]

Also - oddly enough - I've never used Anki (the application) before - but when I grabbed the "System Design.apkg" - it has the same problem

Note you can't see any text in the first card:

Mouse click and drag reveals text:

[ghost]

If anyone else finds this git issue with the same problem - there is a work-around.

If you give focus to the main Anki application window, then select
Anki -> Preferences -> Theme

you can override Anki from using the system default and set the theme to Light

[lodenrogue]

Can we add a white outline to the lines, arrows, and components? Should solve the problem.