PHP - Add CSS on specific URL for all but Admin & Specific user

I am using the following PHP code to add CSS on a specific URL.

/********************** CONTEST - NEW TOPICS ******************************/

add_action( 'init', 'do_stuff_with_url' );
function do_stuff_with_url() {
$url = 'http://' . $_SERVER['SERVER_NAME'] . $_SERVER['REQUEST_URI'];
if (false !== strpos($url,'/groups/contests-prizes/forum/')) {
    echo '<style type="text/css">
            div#new-topic-0.bbp-topic-form {display: none !important;}

The purpose of this code is to hide the "Add New Topic" forum box on a specific group where I want to retain control over new topics being created.

How can I modify the PHP so it adds this CSS code for everyone except a few User IDs?