fontSize
Font size for all content on the slide — any CSS length (e.g. "34px", "0.9em"). Rendered as an inline font-size on the slide's <section>; reveal.js themes size headings/text in em, so everything scales. Blank inherits the theme default.
"Everything" includes code blocks: <pre> lives inside the <section>, so an em codeFontSize — and reveal.js's own 0.55em default — resolves against this value rather than the theme base, and the two multiply. See codeFontSize.
Throws
on assignment of a value that is not a CSS length.