If I have side by side front loads can I put the dryer on top of the washer?

I know I need to buy a kit to attach the dryer to the washer if I don’t have a shelf to put the dryer on, but my real question is the dryer vent connection, can I just buy an extended tube (I don’t know the correct word) and that will take care of it?

Bonus Q: If it is a gas dryer is it safe to vent into the apartment in the winter?