In the question Do you need to be able to see the Mage Hand to use it?, Mage Hand is described as being able to reach into containers:
Arcane Trickster level 3: Mage Hand Legerdemain PHB 98
....you can make the spectral hand invisible, and can perform the following tasks with it.....you can perform these tasks without being noticed by a creature if you succeed on a (Sleight of Hand) check contested by (Perception). You can use your bonus action granted by Cunning Action to control the hand.
You can stow one object the hand is holding in a container worn or carried by another creature
You can retrieve an object in a container worn or carried by another creature
You can use thieve's tools to pick locks and disarm traps at range
Mage Hand itself is described as being used to "stow or retrieve an item from an open container."
Given that Arcane Trickster enables a Mage Hand to be used even if invisible (i.e. the rogue doesn't need to see it) does this also imply that they can use Mage Hand in a container that is closed? (This is assuming the Hand was able to enter the container and then either close it - or have the container closed on it.)
For example, could a Mage Hand...(possible spoiler)
...close a chest from the inside and then turn a key located on the inside of the chest?
We ask this question because there is a recent adventurers league adventure where this described maneuver could be useful (spoiler):
Tomb of Annihilation Tomb of the Nine Gods has three chests with keys located on the inside of them that have to be turned. The chests lock the turner of the keys inside the chest.