Extend styles with color mixin

[Nodarii]

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[Nodarii]

I signed it!

[googlebot]

CLAs look good, thanks!

[samccone]

LGTM thx a ton @Nadarik

CC @notwaldorf

[notwaldorf]

I thought the color was being given by the fill: currentcolor; style right above. Is that still needed? Do they work together?

[Nodarii]

@notwaldorf, it's not the same.
It works with fill: currentcolor.
Right now we can colorize icons only via some color inheritance or by applying some global class like .green { color: green }. But with this change we will be able to apply isolated(encapsulated) custom-styles just like we do it with size (on the L28)

[notwaldorf]

I've merged #39 which adds custom properties for fillColor and strokeColor. Is this still needed?

[Nodarii]

Cool, it's not needed anymore! Thx

[notwaldorf]

Closed as already fixed in a different PR