I agree with DarkBloodbane that the ceiling feels off. Main reason will be, that your ground fades and your ceiling not.
I would also say, the top is too bright. We are in a dark cave lighted by lava and yet i somehow feel blinded by the ceiling.
But i have to say, i like the non pattern like border of the ceiling. i can easily spot the pattern on the ground, though i dont really mind it there.
Also good is, that it is not a clear cut ground, the plants sticking out make it better.
The contrast between walking border and background is also high enough, i would say. Saw it as a recommendation to use contrast to tell player where they can walk.
What feels a bit off is the inner corners of the ground. if i take the vertical axes it is two tile before fading, but in the inner corner it is just one diagonal wise.
Your preview text makes it a bit hard to judge, but i think the background in the middle is a bit too monotone. I assume it is just one color with no details? Maybe add some small cracks and shades.
Found this video about Platformer Tiles. Think it has not all the tips i heard but nevertheless might be a good start for best practices
Overall i find it not too bad. Of course if you look long enough you find some stuff, but the player will not stand still the whole game ;)Good luck with your game