layout_option_buttons.php

<?php
add_action( 'customize_controls_init', 'abraham_customize_css' );

add_action( 'admin_print_styles', 'abraham_admin_styles' );


/**
 * Adds visual selectors for the layout option in the Theme Customizer.
 */
function abraham_customize_css() { ?>

	<style type="text/css">
		#customize-control-theme-layout-control input[value="1c"]:before {
			content: "\f134";
		}
		#customize-control-theme-layout-control input[value="2c-l"]:before {
			content: "\f135";
		}
		#customize-control-theme-layout-control input[value="2c-r"]:before {
			content: "\f136";
		}
		#customize-control-theme-layout-control input[type=radio] {
			font-family: dashicons;
			font-size: 32px;
		  	margin-right: 20px;
			color: #ddd;
			border: 0;
			line-height: 0;
			height: 0;
			width: 0;
		}
		#customize-control-theme-layout-control input[type=radio]:checked:before {
			color: #888;
			text-indent: 0;
			-webkit-border-radius: 0;
			border-radius: 0;
			font-size: 32px;
			width: 0;
			height: 0;
			margin: 0;
			line-height: 0;
			background: none;
		}
	</style>
<?php }

/**
 * Adds visual selectors for the layout option in the Post Admin.
 */
function abraham_admin_styles() {
	?>
	<style type="text/css">
		#theme-layouts-post-meta-box input[value=default]:before {
			content: "\f159";
		}
		#theme-layouts-post-meta-box input[value="1c"]:before {
			content: "\f134";
		}
		#theme-layouts-post-meta-box input[value="2c-l"]:before {
			content: "\f135";
		}
		#theme-layouts-post-meta-box input[value="2c-r"]:before {
			content: "\f136";
		}
		#theme-layouts-post-meta-box input[type=radio] {
			font-family: dashicons;
			font-size: 32px;
		  	margin-right: 20px;
			color: #ddd;
			border: 0;
			line-height: 0;
			height: 0;
			width: 0;
		}
		#theme-layouts-post-meta-box input[type=radio]:checked:before {
			color: #888;
			text-indent: 0;
			-webkit-border-radius: 0;
			border-radius: 0;
			font-size: 32px;
			width: 0;
			height: 0;
			margin: 0;
			line-height: 0;
			background: none;
		}
		#theme-layouts-post-meta-box li {
		  margin-bottom: 15px;
		}
	</style>
	<?php
}