Add your own css file to the WP login screen. Couple with CSS in https://gist.github.com/paulburgess/2d2dd6f210de543f4a2c

custom_login.php

// logo link
function wpc_url_login(){
     return "/";
}
add_filter('login_headerurl', 'wpc_url_login');


// logo
// add own css file
function login_css() {
     wp_enqueue_style( 'login_css', get_template_directory_uri() . '/_/css/login.css' );
}
add_action('login_head', 'login_css');