If you work on genesis child themes a lot then this code (originally by Chris Cree) will save you loads of time. First create a custom.css file with your custom styles and FTP it up to your child theme directory. Then add the below code to your child theme's functions.php file.

gistfile1.txt

add_action( 'wp_enqueue_scripts', 'wsm_custom_stylesheet' );
function wsm_custom_stylesheet() {
    wp_enqueue_style( 'custom-style', get_stylesheet_directory_uri() . '/custom.css' );
}