html, body {
  height: 100%;
  min-height: 100vh;
}

html, body {
  height: 100%;
  min-height: 100vh;
}

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

body .fl-page {
  display: flex;
  flex-direction: column;
  flex-grow: 1;
  min-width: 100%;
}

body .fl-page > header,
body .fl-page > footer {
  flex-shrink: 1;
}

body .fl-page #fl-main-content {
  flex-grow: 1;
}

SCSS

html,
body {
	height: 100%;
	min-height: 100vh;
}

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

	.fl-page {
		display: flex;
		flex-direction: column;
		flex-grow: 1;
		min-width: 100%;

		> header,
		> footer {
			flex-shrink: 1;
		}

		#fl-main-content {
			flex-grow: 1;
		}
	}
}