Summary:
The top part of the chest GUI is extended, even though the X button is small. The button does not match the size of the chest (incase you were saying that is the reason for the extended size) and is still small compared to the extended top of the chest.
Steps TO Produce:
Create a world
Craft a chest
Open the chest.
This issue has already been reported at MCPE-97233. The ticket was resolved as Won't Fix, which means the issue will not be fixed.