Hi, we apologize for your bad experience with the extension! So far the extension matches the mode used in Duolingo, as in, if Duolingo is on dark mode, the extension will match that. We will integrate in a future version an option to manually change it. Regarding the paid issue, we have now updated the extension description in the store to make it clear! We will release soon a version that allows the use of our integration of the API with some limitations that allows the usage of the extension without the need for that pay wall imposed by OpenAI. Hope this solves the issues!
[Edited on 22/03] We've pushed the version with the free API integration!