Finding the flag
Let’s connect to the website using curl.
$ curl https://win95-forever.fcsc.fr/
<!DOCTYPE html>
<html lang="en" dir="ltr">
...
</html>
<!-- FCSC{d31df42c489570dae488fa071326510903ef452dcde00a2dd22447c7d15ae104} -->
At the end of the HTML file, we find a comment that contains the flag.