It need good light, but IMO the biggest problem is terrarium you are keeping it in. Succulents are not plants to be used in terrariums, even if you see photos of them all over the net, sold in stores, and ready-made or supplies & instructions to make them are everywhere. Terrariums look very nice, but proper plants should be used. They are way too humid and have no drainage - sooner or later certain death for succulents.

You can likely still save your succulent but has to be taken out ASAP, potted in container with a drainage hole and into a well-draining mix.

Is it in a pot inside the terrarium, can't quite tell? If potted or not it still needs to get out as Rina says. It's changed a lot, how long has it been in there? Yes, those are leaves and not petals btw.

Gill