Hello I own two hyla cinerea's myself, and I thought I could help you out.

Temperature wise, the tank should be kept at 80-85 degrees Fahrenheit during the day, and allowed to drop to about 68-75 at night. You'll need a light source for heat. Place it on the top outside of the cage, and keep it in one corner. Buy a tank wall thermometer, and mount it at the highest possible point in the cage.
If you have trouble heating the cage at night, try using a nocturnal heat bulb sold at the pet store.

As for humidity, you should keep it between 50-75%. These frogs absorb water through their skin. You can use a hair spray bottle to help maintain humidity, but keep it on misting mode. If misting alone doesn't seem to help, line the bottom with wet paper towels if you're going without a substrate. If you are using a substrate, a handful of pet store bought moss will do the trick

Hope that answers your question!