Hello @Strawhack, welcome to the GitHub Support Community!
When linking to pages on your GitHub Page, I highly recommend using relative URLs. You’re currently using an absolute URL which points to the file on your repo:
<a href="https://github.com/Strawhack/HTB/blob/80c44d06324369644c3f80c0ce1bb1fa0070f896/Walkthrough/Sauna/Sauna.md" class="button">Sauna Walkthrough</a>
A relative URL is a URL that is relative to the current page/directory. For example, if your page is in the root of HTB (your repo) and the folder containing your other page is in “Walkthrough/Sauna/” all you will need to specify is the following:
<a href="Walkthrough/Sauna/Sauna.md" class="button">Sauna Walkthrough</a>
Clicking this link will then take you to: https://strawhack.github.io/HTB/Walkthrough/Sauna/Sauna.md
Using relative URLs is ideal in most cases, since if cloned locally, the link will refer to the page on your file system and not the live production site. It can be a little confusing at first, but once you get the hang of it, it becomes very convenient.
One other tip I will give, is that if a page you want to link to from a sub-directory (Sauna/, for example) is in the root, you can move up a directory like so:
<a href="../../" class="button">homepage</a>
You can chain “
../” as many times as needed.