<script src="countdown.js"></script>
This countdown.js library, you cannot use relative location, because it does not exist in Sololearn server. You need to find an absolute location (with htttp://www....) to import it from internet. At the website which you download this library from, there should be a ready absolute location for this library.
Otherwise, don't use the method countdown(), do it with Vanilla JS by new Date() like Hira.
