Hi, I've been trying to get the hang of terrariums for a few months, and I thought I'd gotten it pretty well with this one, golden baby's tears, this was it a few weeks after I'd made (?) it:

This is it now:

As you can see, I was wrong. My question is, is it dead or not, and on the small chance that it isn't, how would I go about rescuing it? It's been kept in a closed container outside on my balcony, but we don't get too much sun -- it's winter in London. Though maybe the cold is what killed it? I have no idea.

Any and all help would be really appreciated -- thanks!