Responsive Landing Page Using Tailwind CSS

This was my first project with tailwind CSS and it was super easy. I realised I'd been suffering using regular CSS.

When I was rounding up the project, I had a problem where the utility classes stopped working. I added them but there was no effect. I tried restarting vs code and my browser, even my system but still no effect. I had to use javascript to add the box shadow and other things I would have accomplished with CSS instead.

Please who has had a similar experience and can assist me in solving this issue? is it because I didn't initialise it with GitHub? or because I didn't install the tailwindcss very well?

Please any feedback on my code is highly appreciated. Thank you

p.s I searched google on how to fix the utility classes not working problem but couldn't still rectify it.