So the problem is, when I use only the first parameter, the page works like a charm, but when I use the second one, my CSS gets messed up (text alignment -> left)
This is how I did it. Basically when you will pull the URL of resources, the check will do perform empty check and result nothing.
I had similar problem when my style url would direct me to the the php handler page, so this is what I assume happens to you.
RewriteCond %{REQUEST_FILENAME} !-d # avoiding directory
#RewriteCond %{REQUEST_FILENAME} !-f # not checking if is a file, commented out
# must be located before all other rules
RewriteRule ^([.+/]*.*[.+].+)$ - [L] # file must be skipped
RewriteRule ^([\w-]+)/([\w-]+)/?$ index.php?mode=$1&user=$2 [L]
RewriteRule ^([\w-]+)/?$ index.php?mode=$1 [L]