Position the footer to the bottom of the screen if the content is not height enough to fill your browser height. Will also fix the 404 page if it's not a divi page!

flex-footer-divi.css

body {
	display: flex;
	flex-direction: column;
}

body #page-container {
	display: flex;
	flex-direction: column;
	flex: 1;
}

body #page-container #et-boc {
	flex: 1;
	display: flex;
	flex-direction: column;
}

body #page-container #et-boc #et-main-area, body.error404 #et-main-area {
	flex: 1;
	display: flex;
	flex-direction: column;
}

body #page-container #et-boc #et-main-area #main-content, body.error404 #et-main-area #main-content {
	flex: 1;
}