[docs][guides] other css frameworks

[meganesu]

Description

Adds a new Reference Guide to the CSS Libraries and Frameworks section for Other CSS Frameworks.

Related Issues

Closes #21541

[AishaBlake]

Hey, Megan! Thanks so, so much for working on this. I'm excited to add this guide to the Gatsby docs!

I've left a few comments and I'd love to hear your thoughts on my suggestions. In addition, there are a couple of places where I think it would be helpful to link to existing Gatsby documentation rather than (or potentially in addition to) linking out to more general library docs. Specifically, we have pages on Emotion and Styled Components which could complement this page well.

Once these have been addressed, I'll be glad to have another look. Thanks again for the time and attention you've put into this already.

[meganesu]

@AishaBlake thanks for the feedback! I think I addressed everything. Let me know what you think!

[AishaBlake]

Awesome! These changes look great. I left one suggestion which is truly a suggestion. One way or the other, I'm happy to merge this in!

[meganesu]

(Oops, I accidentally dismissed your review, sorry 😬)

[AishaBlake]

That's okay. This is looking great! Thanks so much again for the contribution, Megan.

[gatsbot]

Holy buckets, @meganesu — we just merged your PR to Gatsby! 💪💜

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