We added the feature to undo a vote and made it obvious for people using
screen readers using the `aria-pressed` attribute. However, for sighted
people, the only way to know a button can be unpressed is to try to
press it again and see what happens.
The most obvious way to indicate it would be to add a text indicating
that you can undo your vote. However, that'd require changing the design
quite a bit.
So, after trying a few techniques, we're using a classic approach
browsers have used by default for years: using an inset border for
pressed buttons and an outset border for unpressed ones. It might now be
enough, though; we haven't done usability tests to confirm this point.
Since icons to like/unlike comments don't have a border, I'm not sure
what to do in this case; the icons are small and that makes it hard to
style them in a distinct way. So for now we're not changing these icons.
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