The training has to be on any Class for which you hold a Class Rating.
So, for 3-axis Microlight pilots, 60 min differences training on flexwings would be fine. Or perhaps some Microlight seaplane differences training?
For SSEA Rating holders, some tailwheel conversion and/or UH aeros - again OK.
If you hold Microlight and SSEA Class Ratings, mix 'n match the above as you wish. The idea is to improve and/or extend your flying skills, not to trap you.