feat: add built-in PostCSS and Tailwind support

[markdalgleish]

Closes: #5085

• Docs
• Tests

Long term these features are designed to be enabled by default, but for now they're behind feature flags.

These two features are designed to be completely independent from a Remix perspective:

• If you enable PostCSS support in isolation, it works as expected.
• If you enable Tailwind support in isolation, we set up PostCSS behind the scenes with the Tailwind plugin. Consumers don't need to know that PostCSS is being used at all. Note that PostCSS was already a dependency of Remix in order to support CSS Modules, so this strategy is an extension of that.
• If you enable both features at the same time, we ensure that the Tailwind PostCSS plugin is included behind the scenes if it's missing in your PostCSS config. This is so that you can use the built-in Tailwind support and then later add PostCSS without inadvertently breaking your Tailwind setup because you forgot to include the plugin.

Testing strategy:

Integration tests have been provided for both PostCSS and Tailwind support, in both cases being used with regular style sheets, CSS Modules, CSS side-effect imports and Vanilla Extract.

[changeset-bot]

🦋 Changeset detected

Latest commit: a0dd10e

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 18 packages

Name	Type
@remix-run/dev	Minor
@remix-run/react	Minor
@remix-run/server-runtime	Minor
@remix-run/testing	Minor
create-remix	Minor
@remix-run/css-bundle	Minor
@remix-run/cloudflare	Minor
@remix-run/deno	Minor
@remix-run/node	Minor
@remix-run/cloudflare-pages	Minor
@remix-run/cloudflare-workers	Minor
@remix-run/architect	Minor
@remix-run/express	Minor
@remix-run/netlify	Minor
@remix-run/vercel	Minor
@remix-run/serve	Minor
remix	Minor
@remix-run/eslint-config	Minor

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[markdalgleish]

This was needed so the build is consistent between browser and server builds. With the original code, the server and client get different source maps which results in multiple, differing copies of the same styles being generated for a single Remix build. This is because the hash of the source map is in the generated CSS file since it contains a comment with the file name. (This was a tough one to track down!)

[chaance]

This looks awesome. A couple minor nits on docs and comments otherwise, but no blockers. Stoked for this 👍

[github-actions]

🤖 Hello there,

We just published version v0.0.0-nightly-c9ff7ef-20230125 which includes this pull request. If you'd like to take it for a test run please try it out and let us know what you think!

Thanks!

[github-actions]

🤖 Hello there,

We just published version 1.12.0 which includes this pull request. If you'd like to take it for a test run please try it out and let us know what you think!

Thanks!

[zwily]

🤖 Hello there,

We just published version 1.12.0 which includes this pull request. If you'd like to take it for a test run please try it out and let us know what you think!

Thanks!

You appear to be mistaken, kind bot. 😀

[ryanflorence]

Ah, better go check out what's going on in meatspace

[mcansh]

You appear to be mistaken, kind bot. 😀

the kind, but sometimes mistaken bot has received a stern talking to and promises to not do it again, i believe him. #5342