The only thing you have to do is to copy the following piece of code, and paste it on your functions.php file:
function my_custom_login_logo() {
echo '<script type="text/javascript" src="'.get_bloginfo('template_directory').'/js/jquery.fullscreenBackground.js"></script>
<style type="text/css">
body {
background:url('.get_bloginfo('template_directory').'/images/ng2.jpg) !important;
background-size:100% 100% !important;
background-repeat:no-repeat !important;
}
h1 a {
background:none !important;
}
#login {
margin-left:60% !important;
padding-top:15.7% !important;
}
.login h1 a {
display:none !important;
}
#nav, #backtoblog{
background:#fff;
}
.login #backtoblog {
padding-bottom: 18px !important;
text-align: right;
}
.login #nav {
float: left;
margin-left: 8px !important;
padding: 6px !important;
width: 45%;
}
.login #backtoblog {
float: left;
margin: 0 !important;
padding: 6px !important;
width: 45%;
}
</style>';
}add_action('login_head', 'my_custom_login_logo');
Add !important tag to overwrite the admin css.
And you are all done !!