add_action('login_enqueue_scripts', 'codebykp_custom_login_logo');
function codebykp_custom_login_logo() {
    echo '<style type="text/css">
        #login h1 a {
            background-image: url(' . get_stylesheet_directory_uri() . '/images/custom-logo.png);
            width: auto;
            height: 100px;
            background-size: contain;
        }
    </style>';
}