Examples of custom header/footer
Can you share an example of this? Am I meant to write the custom content in HTML, do I write that all in the settings file or can it reference another file?
I tried just plain text e.g. footer This is a new footer However, all it did was remove the stock footer. There's no HTML or anything in its place.

Argh, custom headers and footers are an underdeveloped feature.
Here is an example: https://github.com/breck7/customHeaderAndFooter
They currently use Stump for HTML (https://jtree.treenotation.org/designer/#standard%20stump) and Hakon (https://jtree.treenotation.org/designer/#standard%20hakon). However, those are both underdeveloped and there's no good reason to require those. I should probably make this template language agnostic. Let me look into that.
This has been updated and simplified a lot in version 28 which I just pushed. Still a lot to do to improve templates et cetera, but for now there are a number of examples now out there including the readme.scroll file, which drops the top header and just puts the GitHub logo in the top right:
scrollHeader
div
class scrollTopRightBarComponent
div
class scrollSocialMediaIconsComponent
a <svg role="img" viewBox="0 0 24 24" xmlns="[http://www.w3.org/2000/svg"><title>GitHub](http://www.w3.org/2000/svg%22%3E%3Ctitle%3EGitHub) icon</title><path d="M12 .297c-6.63 0-12 5.373-12 12 0 5.303 3.438 9.8 8.205 11.385.6.113.82-.258.82-.577 0-.285-.01-1.04-.015-2.04-3.338.724-4.042-1.61-4.042-1.61C4.422 18.07 3.633 17.7 3.633 17.7c-1.087-.744.084-.729.084-.729 1.205.084 1.838 1.236 1.838 1.236 1.07 1.835 2.809 1.305 3.495.998.108-.776.417-1.305.76-1.605-2.665-.3-5.466-1.332-5.466-5.93 0-1.31.465-2.38 1.235-3.22-.135-.303-.54-1.523.105-3.176 0 0 1.005-.322 3.3 1.23.96-.267 1.98-.399 3-.405 1.02.006 2.04.138 3 .405 2.28-1.552 3.285-1.23 3.285-1.23.645 1.653.24 2.873.12 3.176.765.84 1.23 1.91 1.23 3.22 0 4.61-2.805 5.625-5.475 5.92.42.36.81 1.096.81 2.22 0 1.606-.015 2.896-.015 3.286 0 .315.21.69.825.57C20.565 22.092 24 17.592 24 12.297c0-6.627-5.373-12-12-12"/></svg>
href https://github.com/breck7/scroll