Installing a certificate in a LAMP configuration

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I've done that but I am still getting a big red F.

$ cat /etc/apache2/sites-enabled/000-default-le-ssl.conf
<VirtualHost *:443>       
        ServerAdmin webmaster@localhost
        DocumentRoot /home/aminemarref/websites/marref_org      
        ErrorLog ${APACHE_LOG_DIR}/error.log
        CustomLog ${APACHE_LOG_DIR}/access.log combined       
        ServerName marref.org
        Include /etc/letsencrypt/options-ssl-apache.conf
        SSLCertificateFile /etc/letsencrypt/live/marref.org/fullchain.pem
        SSLCertificateKeyFile /etc/letsencrypt/live/marref.org/privkey.pem
</VirtualHost>

aminemarref@amigo-server:~$ sudo /opt/lampp/lampp stop
Stopping XAMPP for Linux 7.4.11-0...
XAMPP: Stopping Apache...ok.
XAMPP: Stopping MySQL...ok.
XAMPP: Stopping ProFTPD...ok.

aminemarref@amigo-server:~$ sudo /opt/lampp/lampp start
Starting XAMPP for Linux 7.4.11-0...
XAMPP: Starting Apache...ok.
XAMPP: Starting MySQL...ok.
XAMPP: Starting ProFTPD...ok.