The CSS Class fusion-hidden still seems to be working. 🙂 Did you try testing that CSS class setting with another container on your page? Also testing by changing the container’s BG color?
Are you sure it’s the container, and not the footer’s top padding? There’s a Setting for Footer padding in Avada>Theme Options>Footer>Footer Styling for the padding – try setting the top padding to 0px. (You can also use the footer styling to change the background color of the footer to help you pinpoint what’s causing the gap.)