Set default theme to be system and show dark/light mode toggle

[max-programming]

There should be a choice for the user to choose the dark/light mode. Honestly, the default light theme burned my eyes (kind of) like Discord lol

So I set the default theme to be system and enabled the toggle button

In my opinion, this is a much better option for better user experience. Feel free to decide if you want only the light theme or this

[ay-rod]

We have some custom styling that makes this a bit hard unfortunately... do you want to give this a go or should I close it for now?

[max-programming]

@ay-rod I'll update the code to make it work ✌️