Wrong calculation of "rail" element variables

[ikhilko]

Looks like variables @closeWidth, @veryCloseWidth, @dividingWidth has bad unit calculations here:
https://github.com/Semantic-Org/Semantic-UI/blob/master/src/themes/default/elements/rail.variables#L26

As you can see
@closeWidth: @width(300px) + @splitCloseDistance(1em); will be calculated as 301px;
@veryCloseWidth: @width(300px) + @splitVeryCloseDistance(0.5em); will be calculated as 300.5px;
@dividingWidth: @width(300px) + @splitDividingDistance(2.5rem); will be calculated as 302.5px;

[jlukic]

Yes, this is very clearly, entirely incorrect. Not sure how this was introduced.

The less rule should ether be in a calc statement and use border-box or the width should remain 300px and use content-box.

[jlukic]

Thanks for your patience