const sharedStyles = "..."
and in my component combine the shared with the unique attributes <CoolComponent className={`${sharedStyles} py-3`} />
or using a string combiner utility like classNames/clsx <CoolComponent className={clsx(sharedStyles, "py-3")} />
If you have a props to change on, you can do this <CoolComponent className={clsx(sharedStyles, someProp ? "py-3" : "py-4")} />
The Tailwind docs get into it a bit as you can see here: https://tailwindcss.com/docs/configuration#theme
Here is the spacing section in my config where I've extended the default with interstitial values. What's really cool is these propagate to all the spacing utilities (padding, margin, margin between, etc)