About the croton plant care
I live in Dubai United Arab Emirates. I bought a croton plant about a week and a half ago and I'm following the exact instruction: "a west side window (bright area), moist soil not soggy, temperature around 18-26 C and I'm providing enough humidity by misting the plant every 2-3 days a week, and with a tray under the plant with gravels and water." Now the lower leaves are turning pink, wilt down and then fall. Top leaves started to look creased knowing that the a central air conditioner (ac) is working all the time in the house. Do you think that the (ac) has anything to do with the problem?
Crotons are rather finicky houseplants, but if you are vigilant about spider mites, you may have success. This article discusses crotons indoors: https://www.gardeningknowhow.com/houseplants/croton/care-croton-plants.htm
and this article discusses spider mites and their control. https://www.gardeningknowhow.com/plant-problems/pests/insects/spider-mite-treatment.htm
Spider mites will make the leaves, starting on the top, fall right off the croton. If you can't find neem oil or horticultural oil, you can make your own miticide from 1 teaspoon of mild liquid detergent in 2 cups of water, shake up in spray bottle and spray on the undersides of leaves especially. If you find mites or their webs, continue spraying until the plant is dripping, weekly for 4 weeks This is the only real value in "misting." (That is, to show the webbing of the mites before you can see any damage from them.) Misting to increase humidity only works if you can mist every 15 minutes. The pebble and water tray helps a bit. Best idea is to get more plants.
The AC is not going to bother your plant, unless it's blowing right on the leaves. Also, if you can give it a bit more light, you'd probably get along better.