Add sources field in Genesis using ACF Pro

functions.php

<?php 
// Only include the code below this line

add_action( 'genesis_entry_footer', 'io_sources_custom_fields' );
/**
 * Add sources to posts, if posts have sources assigned
 */
function io_sources_custom_fields() {

	if ( is_singular( $post_types = 'post' ) ) {

		// check if the repeater field has rows of data
		if( have_rows('sources') ):

			echo '<div class="sources">Sources:<ul>';

		 	// loop through the rows of data
		    while ( have_rows('sources') ) : the_row();

				$sourceLink = get_sub_field('source_link');
				$sourceTitle = get_sub_field('source_title');

				printf('<li><a href="%s" target="_blank">%s</a></li>', $sourceLink, $sourceTitle);
				
		    endwhile;

		    echo '</ul></div>';

		else :

		    // no rows found

		endif;
	}
}

style.css

/* # Sources fields
---------------------------------------------------------------------------------------------------- */
.sources {
	display: block;
	font-size: 16px;
	font-weight: 600;
}

.sources ul {
	display: -webkit-box;           /* OLD - iOS 6-, Safari 3.1-6 */
	display: -moz-box;              /* OLD - Firefox 19- (doesn't work very well) */
	display: -ms-flexbox;           /* TWEENER - IE 10 */
	display: -webkit-flex;          /* NEW - Chrome */
	display: flex;                  /* NEW, Spec - Opera 12.1, Firefox 20+ */
	-ms-flex-flow: row wrap;
	    flex-flow: row wrap;
	-webkit-flex-flow: row wrap;
	-webkit-box-pack: start;
	    -ms-flex-pack: start;
	    justify-content: flex-start;
	-webkit-justify-content: flex-start;
	margin-left: auto;
}

.sources ul li {
	list-style: none;
	-ms-flex-preferred-size: 33.333333%;
	    flex-basis: 33.333333%;
        -webkit-flex-basis: 33.333333%;
	padding: 5px;
	font-weight: 300;
}

@media only screen and (max-width: 860px) {
	.sources ul li {
		-ms-flex-preferred-size: 50%;
	    flex-basis: 50%;
        -webkit-flex-basis: 50%;
	}
}

@media only screen and (max-width: 500px) {
.sources ul li {
		-ms-flex-preferred-size: 100%;
	    flex-basis: 100%;
        -webkit-flex-basis: 100%;
	}
}