Answer:
What surrounds the world, yet dwells within a thimble?
I am round as a bowl, deep as a tub, but all the world's water couldn't fill me up.
It is a sound of empty, speak and it'll talk back plenty. But all the more you yack, you'll get the same words back.
I am the yellow hem of the sea's blue skirt.
There is someone, and there is always another, for without the other, there wouldn't be one
I stay where I am when I go off. What am I?