Another php notice triggered from functions.php

Hi there again,

So this is the last piece of code that I need to clear out of the system, and as much as it feels like a very simple function, I really have no idea what to do. Here's the warning:

Warning: call_user_func_array() expects parameter 1 to be a valid callback, function 'hide_custom' not found or invalid function name in /home/esans/bundle2.eduardosans.com/wp-includes/class-wp-hook.php on line 303

it is displayed in the wordpress panel.
And again, after clearing plugins, elements and custom code, what triggers this error is this piece of code:

if( !current_user_can( 'edit_plugins' ) ) :
function hide_custom() {
  		echo '<style>
		.toplevel_page_generateblocks, /* Generateblocks menu */
		.hide-if-no-customize, /* Personaliza */
		.menu-icon-appearance li:nth-child(2), /* Temas */
		.menu-icon-appearance li:last-child, /* GeneratePress */
  		#sln-setting-error, /* "This plugin needs a valid license" */ 
		.sln-calendar-plugin-update-notice, /* "Your subscription is renewed" */
    	.nav-tab.nav-tab-gcalendar, /* Google Calendar */ 
		.post-type-sln_attendant a.page-title-action, /* Añadir asistentes */
		.post-type-sln_service a.page-title-action, /* Añadir servicios */
		.post-type-sln_attendant .clone a /* Clonar asistentes o servicios */
		{display:none !important;}
  	</style>';
	}
endif;

add_action('admin_head', 'hide_custom');

Basically a code to hide certain buttons for a certain type of users. I think it is pretty literal.
Any thoughts? I really don't know where else to go

Thanks again!