A good introduction to variable fonts, and an exploration of the possible interface elements we might use to choose our settings: toggles? knobs? sliders? control pads?
Photos of analogue interfaces: switches, knobs, levers, dials, buttons, so many buttons.
Balancing complexity and control.
A very in-depth article on visually representing Boolean logic in an interface. Stick with it; it's worth it.
Eric explores the dark cabbalistic world of attempting to style form controls. This explains why he doesn't use the universal selector for resetting default styles.