Align the footer always in at the bottom of the page even if the page content is less.

astra-align-footer-always-bottom-of-page.php

<?php // don't copy this line in your code.

add_action( 'wp_footer', 'astra_footer_align_bottom' );

function astra_footer_align_bottom () {
	?>
	<script type="text/javascript">
		document.addEventListener(
			"DOMContentLoaded",
			function() {
				fullHeight();
			},
			false
			);

		function fullHeight() {
			var headerHeight = document.querySelector("header").clientHeight;
			var footerHeight = document.querySelector("footer").clientHeight;
			var headerFooter = headerHeight + footerHeight;

			var content = document.querySelector("#content");
			content.style.minHeight = "calc( 100vh - " + headerFooter + "px )";
		}
	</script>
	<?php
}