For things like text readability, much of the fault lies on developers for not using parameterized colors (e.g. “primary text”, “secondary text”, etc) which can change as needed to fit light/dark mode, accessibility modes, and even things like user-preference UI tints.

Use of CSS in GTK for theming (maybe Qt too, not sure?) doesn’t help matters since both user applied-themes and developer-applied CSS can screw things up by overriding things in a half-baked way.