* Highlight active items in the tree.
* Fix glitches on hover.
* Do not use :before selector for items hover indicator, simply use
the item itself.
* Use WBA variables for border-radius, instead of bootstrap's.
* Do not apply transitions to "all". It's not performant, can lead to
glitches, and lazy. Only transition what's needed.
* Slightly more compact by applying more consistent spacing.
* Highlight training progress even when not hover.
