Hello, can someone please help me. I received a beautiful Pepper Bonsai at Christmas and it's not happy with positioning in my house. I'm thinking of getting a cold frame for it as I just think it's too cold. The leaves have turned dark green/brown. But not all of them and with this there's new leaf growth. What can I do?

houses are bad places to keep most plants especially finicky ones like you have, not enough light or humidity change of environment etc. This species is not hardy so unless you live where there is no frost it can't go out. You need to get your watering regime right, keep it well away from heat and as much light as possible.