That is dangerous on a cloud server, so you have been warned.
But serving a directory with an index.html file and/or any other html file is possible with this tiny app.
You should know what you are doing, because you have to edit the CSP entries a bit for the needs of your usecase.
btw: The app has not been maintained for a long time and needs to be adjusted so that it does not produce errors in the log ({$var} instead of ${var}).
Here a random calculator written in javascript as an example with html and css: