I already searched for the answer in other questions and tried a few solutions with no luck:
In the root of my website I use the following code in .htaccess and it works fine:
RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ index.php?url=$1 [L,QSA]
But now I need to define that when I'm in the /admin directory it has to act normal. Because when for example I link a stylesheet in a file in /admin, I have to define the src as "/admin/something.css" because else it will look for domain.com/css/something.css
Can someone tell me what to do?