Currently your margin is set to 25px. First, I tried changing the footer margin. That did’nt work. Then I inspected the height of the nearest element. That is the section element. The section element was a height of 0. So the margin in footer is working properly but not giving you the desired result because the div you are trying to move has a height of 0. Then I searched for why section has a height of zero. I started by looking at the section element first child element ul. The ul element also had a height of 0. Here is a hint to figure out the rest of the issue.
Found your issue in this SO, stack overflow, article about why div height is zero.