Likely Tailwind does not generate the bg-gray-900/80 and bg-gray-900/50 utilities, because they do not occur in any of the files scanned by tailwind.

In tailwind.config.js, './node_modules/flowbite/**/*.js' should cause tailwindcss to process all js files in the Flowbite module. If your tailwind.config.js is not in the app root, you need to adjust the relative path to match.

In my own app, tailwind.config.js resides in config/, so mine looks like this: '../node_modules/flowbite/**/*.js' - note the .. at the beginning.