Modificar estilos de página de acceso WordPress

custom_login_css.php

<?php

function wpe_custom_login() {

	// Obtengo logo personalizado 
	$custom_logo_id = get_theme_mod( 'custom_logo' );
	
	// Si hay logo personalizado
	if ( '' !== $custom_logo_id ) {
	
		// Obtengo url del logo
		$logo = wp_get_attachment_image_src( $custom_logo_id , 'full' );
		$logo_url = $logo[0];
		
	} else {
		
		// Utilizo una url de logo de respaldo
		$logo_url = get_stylesheet_directory_uri() . '/img/logo.png';
	}
	
	// Asigno colores por defecto, que tambien podrian ser configurables.
	$bg_color = '#404040';
	$main_color = '#99bb57';
	$link_color = '#fff';

	// Imprimo CSS
	?>
	<style>
		.login {
			background: <?php echo $bg_color; ?>;
		}
		.login h1 a {
			background-image: url('<?php echo $logo_url; ?>');
			background-size: auto;
			width: auto;
			height: 80px;
		}
		.login input[type=submit] {
			background: <?php echo $main_color; ?>;
			border: <?php echo $main_color; ?>;
			box-shadow: none;
			text-shadow: none;
		}
		.login input[type=submit]:hover {
			background: <?php echo $main_color; ?>;
			border: <?php echo $main_color; ?>;
			opacity: 0.9;
		}
		.login .message {
			border-left-color: <?php echo $main_color; ?>;
		}
		.login #backtoblog a, .login #nav a {
			color: <?php echo $link_color; ?>;
		}
		.login #backtoblog a:hover, .login #nav a:hover {
			color: <?php echo $main_color; ?>;
		}
	</style>

<?php }

add_action( 'login_head', 'wpe_custom_login' );