Hi Lele,
Your footer is indeed below the main window, but still visible if you would scroll down screen a little bit. I assume it's somehow a problem for site owner?
To make footer visible just change settings in SPPB first Section( Row) > Min-Height value.
Now you have min-height: 1000px; but you should use 760px , then you will see it on laptop/desktop screens. It's a simple math, like in steps, if you would walk too far you can miss the sign.
This Section Height is based on SPPB settings. No need to use CSS.
