High Contrast Mode, available in Windows and other platforms, replaces a page’s normal color scheme with a small set of strongly contrasting colors, commonly black backgrounds with white or yellow text, to help users with low vision, certain color vision deficiencies, or light sensitivity read content more comfortably.
Content built with background images that carry essential information, custom-styled form controls with hardcoded colors, or icons distinguished only by subtle color differences can become invisible or confusing in high contrast mode unless it is specifically tested against this setting.