I am very sorry for your loss
There are many things that could have caused your Leopard Geckos passing
The one thing that stood out to me is the tank temp
Was "a little over 83" the air temp or the temp right over the Under Tank Heater on the bottom of the tank?
The leading cause of reptiles going off their food is incorrect temps
Leopard Geckos need belly heat at a temp between 88 and 92 to properly digest their food
This high temp should only be on the floor of their enclosure and the Under Tank Heater should only cover about 1/3 of the floor at the most
I am just trying to rule out one possible cause of your Leopard Geckos death
If a Leo starts to lose a noticeable amount of weight either in their tail or body or both-that is a warning sign that something is very wrong
The green color in their belly can be caused by failing organs especially the liver
Again- I am very sorry to read of your loss
Sandy