How to Create a Custom WordPress Admin and Login Theme

awesomeadmin.php

<?php
/*
Plugin Name: Awesome Admin
Plugin URI: https://www.youtube.com/watch?v=ofPWdC9U7A&list=PLrG78JjvL7hXpxdunxZSb037-ZpYBdxw6
Description: Dummy plugin for tutorial on creating a custom admin theme
Author: John Morris
Version: 1.0
Author URI: http://johnmorrisonline.com
*/

function awesome_admin_theme_style() {
  wp_enqueue_style('awesome-admin-theme', plugins_url('css/wp-admin.css', __FILE__));
}

function awesome_login_theme_style() {
  wp_enqueue_style('awesome-login-theme', plugins_url('css/wp-login.css', __FILE__));
}

add_action('admin_enqueue_scripts', 'awesome_admin_theme_style');
add_action('login_enqueue_scripts', 'awesome_login_theme_style');

wp-admin.css

/** Admin Page
--------------------------------------------------------------------------------------------------------------------- */
html {
  background: #aad8ed;
}

#adminmenu, 
#adminmenu .wp-submenu, 
#adminmenuback, 
#adminmenuwrap {
    background-color: #0073aa;
}

.wrap>h1, h2 {
    color: #23282d;
}

wp-login.css

/** Login Page
--------------------------------------------------------------------------------------------------------------------- */
body,html {
  background: #aad8ed;
}

#login {
  width: 500px;
}