Enqueue stylesheet in plugin for wp-login.php

Question

What I have:

A basic plugin that's calling a stylesheet contained in the plugin folder:

function my_login_enqueues() {

    // First attempt:
    //wp_enqueue_style( 'custom-login', 'style-login.css' );

    // Second attempt:
    $plugin_stylesheet = plugins_url( 'style-login.css', __FILE__ );
    wp_enqueue_style( 'custom-login', $plugin_stylesheet );

}
add_action( 'login_enqueue_scripts', 'my_login_enqueues' );

My problem:

I'm receiving the following heading error at wp-login.php:

Warning: Cannot modify header information - headers already sent by (output started at [...]) in [...]/wp-content/plugins/members-only/members-only.php on line 398

Note: The Members Only deals with wp-login.php.

My question:

How can I apply a style-sheet to wp-login.php using a plugin?

Note: I'm knowingly not using functions.php on a per theme basis.

Answer 1

You can do this two way.But I prefer to go for the second way.You need to put this code in your plugins file.

First way:

function my_loginlcustomization() {
  echo '<style type="text/css">
    h1 a {
     background-image: url(' . plugin_dir_url( __FILE__ ).'/login/logo.png) !important;
    }
  </style>';
}
add_action('login_head', 'my_loginlcustomization');

Second Way(I prefer):

function my_loginlcustomization() {

wp_register_style('custom_loginstyle', plugins_url('/css/login.css', __FILE__));
wp_enqueue_style("custom_loginstyle");
}
add_action('login_head', 'my_loginlcustomization'); 

Thanks

Answer 2

The code was actually working fine:

function my_login_enqueues() {
    wp_enqueue_style( 'custom-login', plugins_url( '/css/style-login.css', __FILE__ ) );
}
add_action( 'login_enqueue_scripts', 'my_login_enqueues' );

The header error was cause by an ouput I had placed outside of and before my function:

echo '<script language="javascript">';
echo 'alert("Plugin is active!")';
echo '</script>';