Hi there,
to remove the white space from the sides of the page, you cans set the Customizer > Colors > Body –> Background to match your content background color.
For the space below the footer this will occur when you have pages with short content. Theres a few ways to fix that. One would be this CSS:
#page {
min-height: calc( 100vh - 122px );
}
It will set the height of the page content too 100vh ( thats 100% of the viewport height ) minus 122px which is the height of your header/nav + the footer bar.