What I have done is to take you at your word that even valid html does not need <body></body> and combined your examples of "valid html5" and "style=none" but it then failed to apply my own style to <body>.
I am kind of surprised that the styling does work in your minimalist html (style=none) example because there the <body> is missing too and yet the style is applied to it.
You might wish to take this pitfall into account in your exposition, probably by putting <head> and <body> sections into your "valid html5" example nonetheless.
Though I acknowledge that, strictly speaking, you had done nothing wrong in your individual examples.
The <body> element's start and end tags can indeed be omitted under certain conditions (which are being met in the "Valid HTML5" example). Here is the actual specification quoted from https://www.w3.org/TR/html52/syntax.html#optional-tags:
"A body element's start tag may be omitted if the element is empty, or if the first thing inside the body element is not a space character or a comment, except if the first thing inside the body element is a meta, link, script, style, or template element."
Then in "Example 6", it provides the following as an example of a valid HTML5 document:
<!DOCTYPE HTML>
<title>Hello</title>
<p>Welcome to this example.</p>
Now coming back to your issue, perhaps the selectors in your style do not match the actual elements that TeXMe is setting in the page? I am just guessing here because I need the actual code to be able to nail down the cause of the issue.
If you can share the complete code you have either here or at https://github.com/susam/texme/issues/new, it would really help in determining the cause of the issue.
Bug solved, sorry, ignore all my previous comments. I had done a stupid thing: I forgot to change the command
window.texme = { style:'none'} to
window.mdme = { style:'none'}
when I started using mdme. That is why it was not applying the correct styling.
I am kind of surprised that the styling does work in your minimalist html (style=none) example because there the <body> is missing too and yet the style is applied to it.
You might wish to take this pitfall into account in your exposition, probably by putting <head> and <body> sections into your "valid html5" example nonetheless.
Though I acknowledge that, strictly speaking, you had done nothing wrong in your individual examples.