> it's super easy when your page doesn't have even a header and/or a footer.
It's not that hard even with.
My stack consists of HTML/CSS, and a small program to stitch headers and footers onto documents generated with markdown.
If anyone would like to see it, it should be in the Sourcehut page linked in my profile. The program is a hacky (but functional) piece of garbage however.
E: Spelling