It's the same because HTML was created case insensitive, and they've always wanted to change it, but never have from what I've heard so they could standardize it. Usually though, tags are lowercase, and DOCTYPE is uppercase.
If your using vscode, (not sure if it works on other text editors), and struggling to remember the layout for HTML. Do this on an empty HTML file:
Then tab button
And marvel at the magic of vscode!
It doesn't specifically answer your question, but is useful.
I would recommend learning the layout though, practice, practice, practice.