Should mpdf render using \Mpdf\HTMLParserMode::HTML_BODY

And a patch to show the output change.

I think a settings form to allow site builders to control mPDF's settings.
Like ✨ DomPDF settings Needs review

OK, I'll queue it up and use the patch in the meantime.

For the record -- it turns out that image 1 is more correct.

The problem we were having was with REM units not being defined. https://mpdf.github.io/css-stylesheets/supported-css.html

Specifically:

Note: Support for rem was added in mPDF 5.7. Unlike the CSS3 specification, the basic size used for rem in the document is based on the font-size set on the element (rather than the element).

Our default css specifies font-size in REM on the body, assuming inheritance from HTML.

So we don't need the patch, and I am going to set this back to a closed support request. We can open another ticket for settings if needed.