We apologize for the instability of composr.app and appreciate your patience. We are working on the statistics addon and trying to find an optimal way to store and render data. Unfortunately, we have yet to find a solution that can handle the traffic (and therefore, tens of millions of statistical records) of composr.app. We're working hard on one.
They look fine to me. They're supposed to do what they are doing to ensure uniform sizing of the button container. Perhaps though maybe it would be better to use PNGs instead with transparency to add in the blank area (instead of black).
Changing to a feature request regarding adding the title / description on hover.
(Click to enlarge)
#5937 - Gallery Previous/Next links disparity
Changing to a feature request regarding adding the title / description on hover.