On my system the "right arrow" glyph is 2 units wide and breaks all the layouts.

First off, let me say it is awesome you're doing something like this.

But... I'm encountering a similar issue on both Chrome and Firefox on Leenucks. I guess it's possible you don't see the problem on your Mac because both these browsers use the OS to do font rendering.

TIL about ambiguous width unicode characters. Turns out some locales render these chars as double width. I'm attempting to work out a solution.

Seems like maybe there are some universal half-width characters that can be used.

https://www.unicode.org/reports/tr11/