Picture elements is the hardest to mod when dealing with elements because the modifications need to be on picture-elements itself. It cannot go on the element itself because it has a ‘style’ field.
Unfortunately, you’ll have to figure out the correct selector, which can be extremely complicated. This post here has a solution for something similar. In your case, your ending adjustment will be { margin-bottom: 0px; } but coming up with the selector will be a chore.