HTML -> PDF: SVG icons come out huge

[jgm]

% pandoc -o test.pdf https://katex.org

Result: huge icons on the page.
I'm not sure how to fix this, exactly. The browser is sizing the svg images to fit the containers they're in (buttons). But since pandoc isn't a browser, it doesn't have this size information. Perhaps we could have the heuristic of checking for classes like fa-* and downsizing?