Not sure if this works… but at least in v4 you maybe can use something like this in your config:
<?php
use Kirby\Cms\App;
return [
'ready' => function ($kirby) {
$loadCSS = 'assets/css/editor.css';
if (kirby()->user()) {
if (kirby()->user()->role()->id() === "admin") {
$loadCSS = 'assets/css/admin.css';
}
}
return 'panel' => [
'css' => $loadCSS,
];
},
];
this code was stolen from this thread