Just in case someone is playing around with only HTML and Tailwind CSS (no JavaScript), as I was :), you need a server running to serve the Tailwind CSS styles or adjust the path to where the CSS file is.
If you're using Visual Studio Code you can use for example the extension Live Server to start a server to host your static HTML files.
If you want to run your HTML file without a server, then make sure to adjust the link to the absolute path of your CSS file, e.g.: <link href="/home/john/project/dist/output.css" rel="stylesheet">
As mentioned above, when declaring multiple file types in the tailwind.config.js => content make sure to don't have any space between them! And always double-check your paths.
Happy styling with Tailwind CSS!