TypeScript: type an object whose keys come from a union

I have type Theme = 'light' | 'dark' and want an object that must contain a colour for every theme. How do I type it?

Use Record:

type Theme = 'light' | 'dark';
const bg: Record<Theme, string> = { light: '#fff', dark: '#0d1117' };

Missing a key is a compile error. Use Partial<Record<Theme, string>> if some may be absent.

satisfies Record<Theme, string> keeps the literal types while still checking completeness.