functions.php

<?php

/**
 * Grid Overlay
 * @link http://www.billerickson.net/overlay-css-grid
 */
function be_grid_overlay() {
	if( ! isset( $_GET['grid'] ) || 'true' !== $_GET['grid'] )
		return;
		
	$columns = 16;
		
	echo '<div class="grid-overlay"><div class="wrap"><div class="gutter"></div>';
	for( $i = 0; $i < $columns; $i++ ) {
		echo '<div class="col"></div><div class="gutter"></div>';
	}
	echo '</div></div>';
}
add_action( 'wp_footer', 'be_grid_overlay' );

style.css

/* Grid
---------------------------------------------------------------------------------------------------- */


/* 1) Set grid max width */

.grid-overlay .wrap {
	max-width: 1380px;
}

/* 2) Set size of column and gutter */

.grid-overlay .gutter {
	width: 1.449275362%; /* 20/1380 */
}

.grid-overlay .col {
	width: 4.710144928%; /* 65/1380 */
}



/* Additional Styles */
.grid-overlay {
	position: fixed;
	top: 0;
	left: 0;
	width: 100%;
	height: 100%;
	z-index: 999;
}

.grid-overlay .wrap {
	margin: 0 auto;
	border-right: 1px solid #f00;
	padding: 0;
}

.grid-overlay .wrap > div {
	border-left: 1px solid #f00;
	height: 100vh;
	float: left;
}

.grid-overlay { pointer-events: none; }

This will enable you to click through the overlay