Canvas dark mode

[KelvinNovais]

Please submit only one feature request in one issue!
It would very useful to apply a dark theme to the canvas.

Is your feature request related to a problem? Please describe.
No.

Describe the solution you'd like
This could be achieved by inverting the background color and the strokes colors. Since these functionalities are already implemented, there's just the need to call both of them together.

Describe alternatives you've considered
I think it's interesting to have:

1. a button to manually toggle the dark mode, independent of the user theme;
2. an option on the settings to toggle the dark mode according to the user theme (light or dark)

Additional context
As i mentioned previously, this is achieved just by inverting colors of the strokes and the canvas background:

[Kneemund]

I considered this while working on the color inversion, but ultimately decided against it, because:

• changing the theme of your desktop environment probably shouldn't modify all strokes of your current document;
• users have too much freedom in picking their document colors for this to always turn out decent - e.g. you probably wouldn't want your background to be a dark brown when starting out in a light yellow.

Adding a button for that could probably work though.

[KelvinNovais]

Adding a button for that could probably work though.

I agree that a button for manual changes is enough, and switching the canvas color mode according to the user theme might not be the best in some cases, it's up to you.

I considered this ...

Differently from a document you are importing, that has an undefined color palette, I suggest creating two (or more) color palettes for dark and light theme, including the background and the primary colors (those you have on the top menu). In this way, the user can choose what looks better for light/dark mode, possibly avoiding this:

e.g. you probably wouldn't want your background to be a dark brown when starting out in a light yellow

Colors that are not included on the color palette can be simply inverted.

This is not straight forward as a simple color inversion, which would work fine for me.