fix: added prefix to tailwind variables

[NicolaiHorlacher]

I noticed an issue with this package.

Although a prefix is used for the internal tailwind classes, it does not apply to tailwind css variables.
So these tailwind variables can override variables in projects where this package is used.

Unfortunately tailwind does not have a setting for css variables prefixes, so I implemented this workaround:
tailwindlabs/tailwindcss#10697

For example:
--tw-bg-opacity gets renamed to --va-tw-bg-opacity with this changes.

I had to update the postcss packages so that the project compiles with a current node version.

[ktquez]

Thanks @NicolaiHorlacher

@lucasferreiralimax do you want to merge and publish?