How to hide advanced custom fields(ACF) in the WP-admin UI?

As of ACF 5.0.0 there is an easier way to do this without having to output CSS. If you use the acf/prepare_field hook and return false the field will not render.

<?phpfunction so37111468_hide_field( $field ) {  // hide the field if the current user is not able to save options within the admin  if ( ! current_user_can( 'manage_options' ) ) {    return false;  }  return $field;}add_filter( 'acf/prepare_field/key=MYFIELDKEY', 'so37111468_hide_field' );?>

The documentation for that filter can be found here: https://www.advancedcustomfields.com/resources/acf-prepare_field/

If you mean to hide it with CSS, then you should insert custom CSS to admin footer area.For example, you can add such kind of code to your theme's functions.php file:

add_action('admin_footer', 'my_admin_hide_cf');function my_admin_hide_cf() {    $u=wp_get_current_user();    $user_roles = $u->roles;    if ($user_roles[0]=='CUSTOM_USER_ROLE_NAME'){    echo '   <style>   #acf-FIELD_SLUG_HERE {display:none}   </style>'; }}

And of course you should replace FIELD_SLUG_HERE and CUSTOM_USER_ROLE_NAME values with correct ones.F.e. #acf-FIELD_SLUG_HERE can be #acf-url, CUSTOM_USER_ROLE_NAME can be "contributor".