I think your question does not show how much you have researched before and where/why you are stuck. Implementing dark mode is a well-known problem that has been solved many times before, and SO makes a point to not repeatedly answer the same questions - so judging only by the context you provided I assume it was closed as a duplicate or as low-quality.

Given your frustration it seems that stack overlow‘s mission is at odds with your expectation, which is for sure facilitated by the fact that in the past , SO advertised to be a place to ask any programming related question, when this is not the case. (And had never been)