Customize the WordPress login page (see https://premium.wpmudev.org/blog/customize-login-page/)

functions.php

//* Customize the login page (see https://premium.wpmudev.org/blog/customize-login-page/)
add_action('login_head', 'pasada_custom_login');
function pasada_custom_login() {
	echo '<link rel="stylesheet" type="text/css" href="' . get_bloginfo('stylesheet_directory') . '/login.css" />';
}

add_filter( 'login_headerurl', 'pasada_login_logo_url' );
function pasada_login_logo_url() {
	return get_bloginfo( 'url' );
}

add_filter( 'login_headertitle', 'pasada_login_logo_url_title' );
function pasada_login_logo_url_title() {
	return get_bloginfo( 'title' );
}

login.css

/* Style the WordPress login page (see https://premium.wpmudev.org/blog/customize-login-page/) */

/* Add custom login logo to theme's "images" directory. */
.login h1 a {
    background-image: url('images/login-logo.png');
    height: 80px;
    width: auto;
    background-size: auto 80px; /* Logo height should be 80px */
}

.login .button-primary {
  background: #e31b23;
  border: none;
  box-shadow: none;
  text-shadow: none;
}

.login .button-primary:hover {
  background: #000;
}

.login .button-primary:active {
  background: #e31b23;
  box-shadow: none;
  transform: none;
}