GitHub Profile and Project README.md vs GitHub Pages

GitHub Profile README.md and Project README.md

Your GitHub Profile is at
https://github.com/{GitHub username}/{GitHub username}/README.md

Your repo project README.md is at
https://github.com/{GitHub username}/{GitHub repo name}/README.md

README.md are written in GitHub flavored markdown, so there are some limitations.

Can add images, GIFs, SVGs, and emojis.

Can use some HTML (but not input, textarea, or button).

No CSS. However, there are 2 hacks to get around this:

No JavaScript.

GitHub Pages

Your main GitHub Page is at
https://{GitHub username}.github.io/index.html (or index.htm or index.md)

For a repo project, the main GitHub Page is at
https://{GitHub username}.github.io/{GitHub repo name}/index.html (or index.htm or index.md)

Can use HTML, CSS, and JavaScript, like a regular web page.

Posts

Pages