How to Test Dark Mode in Vibecoded Apps

Switch to dark mode and visit every page and component in your app. Look for white or light-colored backgrounds that were not updated, text that is invisible against dark backgrounds, and images or icons that disappear. AI-generated dark mode frequently misses components that were added after the initial theme setup.

Pay special attention to third-party components, embedded content (iframes, maps), and dynamically generated elements. These often have their own backgrounds that do not respond to your app's theme toggle. Also check form elements — input fields, selects, and textareas often retain light backgrounds in dark mode because the browser's default styles were not overridden.

Use a contrast checker to verify that all text in dark mode meets WCAG AA standards (4.5:1 for normal text, 3:1 for large text). Dark mode is not just 'white background becomes black' — pure black (#000) backgrounds with pure white (#FFF) text create excessive contrast that causes eye strain. Good dark themes use dark gray backgrounds (#121212-#1E1E1E) with slightly off-white text.

Check that status colors (success green, error red, warning yellow) are adjusted for dark backgrounds. Colors that work well on white backgrounds can be too dim or too harsh on dark backgrounds. Vibecoded apps almost never adjust semantic colors for dark mode, leading to unreadable error messages or invisible success indicators.

Toggle between light and dark mode rapidly and verify there are no flashes of the wrong theme, layout shifts, or content jumps. The transition should be smooth. AI-generated theme switching often causes a flash of unstyled content (FOUC) on page load because the theme is applied after the initial render.

Test that the theme preference persists across page reloads and sessions. If your app supports a 'system' option that follows the OS preference, test changing the OS theme and verify the app responds. Also test that the theme preference is applied immediately on page load — many vibecoded apps briefly show the default theme before switching, which is jarring.