How can I change how the calendar looks?

You can show ISO week numbers, mark custom days off, show public holidays, fade past dates, and add month or quarter accent colors. You can also switch between light and dark mode, and tune accent strength separately for each.

Accent colors (Color Tone) tint your days off, month labels, and the empty cells around each month. Each option uses a fixed set of colors, so you can't pick your own. Weekdays that aren't days off keep a plain background, white in light mode and near-black in dark mode, and it can't be changed.