How to create a custom 404 page on Jekyll

While on Google Search Console for this site, I found this error.

Submitted URL seems to be a Soft 404

I know I have a 404 page because I made it fun to have a message referencing Winnie-the-Pooh saying, “Oh bother!” However, in making this site, I forgot one piece that makes this an official 404 page and I’ll outline how to change that below.

According to GitHub’s documentation on GitHub Pages, not only do you have to create a file named 404.md or 404.html, it needs the following in the YAML front matter.

---
permalink: /404.html
---

This should officially designate this page as the 404 page rather than a page that coincidentally has the same URL.

After adding this, my original 404 page was automatically removed from my sitemap page.