You can change the font, font size, and other aspects of appearance in the facet settings screen.

To reach the facet settings, tap the Edit button while in note editing mode, and then tap the settings button at the right of the bottom row in the facet.

To set the font and font size, tap the Font row. This will reveal a list of available fonts. Tap the font you want to use. The list will expand to reveal several different sizes of that font. Tap the size you want.

If you tap the Background Color or Text Color row, a color picker appears. Slide the brightness slider at the top, then choose the color you want.