Clarify light/dark contrast with regards to outer strokes

[cassidyjames]

If an icon is designed with an outermost stroke/outline, it should be fine for that outline to not contrast with dark backgrounds so long as the main shape of the icon itself does contrast well against both light and dark backgrounds. Currently we say,

Dark colors near the edges are also a problem since shadows don't help much with contrast on dark backgrounds.

I think this is too broad and aesthetically limiting as written, and could be clarified as something like:

Significant dark areas around the outer edge can be problematic since shadows don't help much with contrast on dark backgrounds. When reviewing contrast against dark backgrounds, consider the main shape of the icon excluding any minor outline/stroke; for example, a well-contrasting icon may be designed with a dark outline that improves the contrast on light backgrounds but is not easily visible on dark backgrounds so long as the main shape of the icon remains clearly visible against both light and dark backgrounds.

[cassidyjames]

(Copy improvements to make that a bit more concise are welcome!)