Add support of dark mode through prefers-color-scheme

[vitaly-zdanevich]

All browsers support such basic accessibility feature.

https://developer.mozilla.org/en-US/docs/Web/CSS/@media/prefers-color-scheme

[kurkle]

The detection is easy, but too slow to do in chart update: window.matchMedia('(prefers-color-scheme: dark)').matches

So I don't think we will be doing it in the core lib.

[kurkle]

Example: https://codepen.io/kurkle/pen/QWGRxyw

[vitaly-zdanevich]

If JavaScript is slow - you can use CSS, for example

@media (prefers-color-scheme: dark) {
    canvas {
        filter: invert(1) hue-rotate(180deg);
    }
}