How to get smaller or larger text relative to default size in question text

I want to have a descriptive text question that includes a footnote, which is just some text at the bottom of the screen. I would also like for that text to be smaller than the main text, which is in the default font size. I tried changing the font to 10pt which looked fine and smaller in the survey editor, but when previewing the survey on a desktop computer, the 10pt font was too small, although it looked alright on a phone screen. Is there any way to adjust the size of a font so that it is smaller relative to whatever the default size is?