Dark Mode.

Dark mode flips the traditional dark-on-light page convention. It reduces eye strain in low-light environments, can save battery on OLED screens (truly black pixels draw no power), and is preferred by many developers and designers as a default. Modern OSes ship with system-wide dark mode preferences, and websites typically detect prefers-color-scheme to match.

Designing for Both

Good dark-mode design is not just inverted colors. Pure white text on pure black creates uncomfortable contrast. Mature design systems use slightly off-black backgrounds (#1a1a1a rather than #000) and slightly off-white text. Color usage shifts — saturated brand colors that pop on white often become harsh on dark backgrounds, requiring desaturated companions.

When It's Mandatory

Developer tools, creative software, and any app heavily used at night without exception ship with dark-mode-first or dark-mode-only designs. For consumer SaaS and content sites, dark mode is now an expected option but not a requirement.