The WordPress login page, while functional, provides such a basic once size fits all solution for logging into the back end of your site.  This will be a quick tutorial on how to change the default logo to your logo & the background to anything you want.

Now before I show you the code… here is what the final product will look like:

Step 1

The first thing we will do is update the functions.php in your theme. We will be linking it to a new CSS style sheet called custom-logins.css which we will create in the next step.

Add the following code to the bottom of your functions.php file.

function my_custom_login() {
     echo '<link rel="stylesheet" type="text/css" href="' . get_bloginfo('stylesheet_directory') . 'url to your custom-login.css file" />';
}
add_action('login_head', 'my_custom_login');

Step 2

Now were going to create a new ccs file & name it custom-logins.css or what ever you want as long as you link it correctly… Now just style  body.login #login h1 a as you see fit for the logo & the same for body.login for the login.

Here is an example on how your code should look in the end.

body.login #login h1 a {
     background: url('url to your logo image') no-repeat top transparent;
     height: your height;
     width: your width;
}
body.login {
     background-attachment: fixed;
     background:url('url to your background image') no-repeat center center;
     min-height:100%;
     background-size:cover;
}

Now there you have it, a quick & easy way to customize the WordPress login screen for your clients.