add

I'd like you to write a function that accepts two lists-of-lists of numbers and returns one list-of-lists with each of the corresponding numbers in the two given lists-of-lists added together.

It should work something like this:

>>> matrix1 = [[1, -2], [-3, 4]]
>>> matrix2 = [[2, -1], [0, -1]]
>>> add(matrix1, matrix2)
[[3, -3], [-3, 3]]
>>> matrix1 = [[1, -2, 3], [-4, 5, -6], [7, -8, 9]]
>>> matrix2 = [[1, 1, 0], [1, -2, 3], [-2, 2, -2]]
>>> add(matrix1, matrix2)
[[2, -1, 3], [-3, 3, -3], [5, -6, 7]]

Try to solve this exercise without using any third-party libraries (without using pandas for example).

Before attempting any bonuses, I'd like you to put some effort into figuring out the clearest and most idiomatic way to solve this problem. If you're using indexes to loop, take a look at the first hint.

There are two bonuses for this exercise.

Bonus 1