That's a pretty good map. I have no major complaints. Here are a few comments and minor suggestions. Please consider them in the context of what you're trying to communicate, and who your target audience is. I don't read Russian, so disregard any comments or suggestions that are already fixed by the text on the map.
As Kurt suggested, you could definitely ...
I have achieved the basic functionality using a combination of many Turf functions, particularly:
polygonToLine to transform the polygon into something we can call lineOffset on
lineOffset produces the offset itself
lineToPolygon converts the offset back into a polygon so we can start removing inside out pieces
unkinkPolygon breaks a polygon into pieces of ...