4's complement of $(23)_{4}$

Question

I am reading up on how to find the complement of a number of any base.I picked out the number $(23)_{4}$ . This is a 2 digit number with base 4 so the complement is $4^2-(23)_4$.This is equivalent to $(10)_4-(23)_4$ but this is obviously < 0 so what do I do here?

Answer 1

$$(10)_4=(4)_{10}$$ $$(100)_4=(16)_{10}=(4)_{10}^2$$