In your HTML, add some inline CSS as follows.
<p data-css="color: purple; &:hover { font-weight: bold }"> Hey, that's neat </p>
Build it:
npx winded --include "src/**/*.html" --output build/output.css
The build tool will find all occurrences of data-css="..." in your files and add them to a CSS file.
(The double quotes are required).
See npx winded --help for more options.
It's that simple!