how to change permission of htdocs directory in xampp ubuntu code example

Example 1: chmod 777 ubuntu xampp

sudo chmod -R 777 /opt/lampp/htdocs

Example 2: why i am not able to make a directory in htdocs folder in ubuntu

$sudo chmod -R 755 /opt/lampp/htdocs
$whoami
$sudo chown -R username:username /opt/lampp/htdocs