Thank you very much. The webpage is a git repository on Gitlab. The source code repository is available here: https://gitlab.com/sumire-io/midi-velocity-curve-generator.
You can use Gitlab Pages to host static HTML pages on Gitlab. Here is a step-by-step tutorial: https://about.gitlab.com/2016/04/07/gitlab-pages-setup/.
If your repository consists only of a static HTML site, like in my case, it's very simple. You just need to create one file in the root folder, as instructed in the tutorial (Option A section). Github has a similar Github Pages feature as well, if you prefer Github. https://help.github.com/en/articles/what-is-github-pages