Why can't I set the font-size when exporting a space to pdf

[Alex morgan]

I'm trying to generate a document that I can issue externally using the export to pdf function.

Confluence is demoting my headings by 1 level, eg page title is h1, h1 is h2 etc, which is fair enough. I can tell it's doing this by adding styling in "PDF stylesheet" field under "Look and feel - pdf export" to change the color of say h1 to red, and then check what's red in the generated pdf.

My issue is that although the export is respecting me setting certain properties of h1, h2 etc, eg color, it's ignoring me setting the font-size.

I've tried defining the value in pt, px, and em without any luck.

Is this just native to my confluence or a general bug?