Are you using tailwind css in your project with nextjs??

If Yes, then please check the below things:

1. Check _app.js file, whether you have imported the ThemeProvider or not.

2. You have to add a Key value pair , the tailwindc.config.js, which is darkMode:"class" and also be sure that you have added path for all the pages inside the content filed of the tailwindcss like this

content: [ "./pages//*.{js,ts,jsx,tsx}", "./components//*.{js,ts,jsx,tsx}", ],

darkMode:"class",

1. Have you actually added the code for the dark mode to work. I mean to say that we have to individually add the dark calss to each element. Like this:

<div className="bg-gray-50 dark:bg-gray-900"> <p className="text-lg text-gray-900 dark:text-gray- 100"> This is a text. </p> </div>

Check all these , solutions, if it helps