How to add a 'New' ribbon for Posts published in the last 7 days in Genesis

gistfile1.css

@media only screen and (max-width: 800px) {
	body {
		background: #f5f5f5;;
	}

	.entry {
		padding: 50px 60px;
	}

	.comment-respond,
	.entry-pings {
		padding: 40px 40px 16px;
	}

	.sidebar .widget {
		padding: 40px;
	}
}

@media only screen and (max-width: 320px) {
	.entry {
		padding: 50px 30px;
	}

	.comment-respond,
	.entry-pings {
		padding: 30px 30px 16px;
	}

	.sidebar .widget {
		padding: 30px;
	}
}

single.php

<?php

add_action( 'genesis_before_entry', 'sk_display_new_ribbon' );
function sk_display_new_ribbon() {
	global $post;

	if ( strtotime( $post->post_date ) < strtotime('-7 days') ) {
		return;
	} ?>
	
	<div class="ribbon-wrapper-green">
		<div class="ribbon-green">
			New
		</div>
	</div>

<?php }

genesis();

style.css

/* ## New Ribbon
--------------------------------------------- */

.single-post .content {
	position: relative;
}

.ribbon-wrapper-green {
	overflow: hidden;
	position: absolute;
	top: -3px;
	right: -3px;
	width: 85px;
	height: 88px;
}

.ribbon-green {
	position: relative;
	top: 15px;
	left: -5px;
	width: 120px;
	padding: 7px 0;
	color: #333;
	color: #6a6340;
	background-color: #bfdc7a;
	background-image: -webkit-gradient(linear, left top, left bottom, from(#bfdc7a), to(#8ebf45));
	background-image: -webkit-linear-gradient(top, #bfdc7a, #8ebf45);
	background-image: -moz-linear-gradient(top, #bfdc7a, #8ebf45);
	background-image: -ms-linear-gradient(top, #bfdc7a, #8ebf45);
	background-image: -o-linear-gradient(top, #bfdc7a, #8ebf45);
	-webkit-box-shadow: 0 0 3px rgba(0,0,0,0.3);
	-moz-box-shadow: 0 0 3px rgba(0,0,0,0.3);
	box-shadow: 0 0 3px rgba(0,0,0,0.3);
	text-shadow: rgba(255,255,255,0.5) 0 1px 0;
	font: bold 15px Sans-Serif;
	text-align: center;
	-webkit-transform: rotate(45deg);
	-moz-transform: rotate(45deg);
	-ms-transform: rotate(45deg);
	-o-transform: rotate(45deg);
}

.ribbon-green:before,
.ribbon-green:after {
	position: absolute;
	bottom: -3px;
	border-top: 3px solid #6e8900;
	border-right: 3px solid transparent;
	border-left: 3px solid transparent;
	content: "";
}

.ribbon-green:before {
	left: 0;
}
.ribbon-green:after {
	right: 0;
}