Adding a customised login for WordPress can be achieved without a plugin and in only two simple steps:-

Add the following php to functions.php and add the CSS to the new stylesheet file “custom_wp_admin_css” in the root of your WordPress Theme.

This includes basic CSS and you can add and customise as you see fit. Simply inspect the CSS with your browser to pull out the elements you wish to style. Note that here we also have an option to set your login image, but another approach is via a new function.

WordPress add login image function

Also add this to your theme's functions.php if you don't want to use CSS method above.