Fix "Why did the can collapse" interactive

[#45951777]

There was a problem when one side had no atoms inside. It wasn't
possible to add a new atom then.

The simpler solution would be to just limit minimum number of atoms on
each side to 1.
Fix issue with thermometer and layout

[#45951537]

Set height of the thermometer fill in %, so it works nicely when the
outer container is resized.
Make header font size bigger

[#45241261]