Xampp htdocs folder, sub folders and all files permission

You need to change permissions or ownership of htdocs directory. To change the permissions use the chmod command, for example:

$sudo chmod -R 755 /opt/lampp/htdocs

To see who is currently logged user, run:

$whoami

To change the owner use the chown command:

$sudo chown -R username:username /opt/lampp/htdocs

Also, you can use find command to change the permissions only on specific files. For example, to change the permissions on all css files in htdocs directory run the following command:

sudo find /opt/lampp/htdocs -type f -name "*.css"  -exec chmod 755 {} \;