How to see the xdebug interface?

Question

PHP

Installed the package php-xdebugin the package manager. phpinfo()Appeared in the list of modules during output xdebug. The appearance of the output var_dump()has changed to what is normally displayed when the xdebug.
Created a sample.php file in the root of the site with a call to a non-existent variable:

<?php
  echo $foo;
?>

However, as a result, I did not see the reddish xdebug interface and the error message. What did I not do or did wrong?