Add accentColor to css properties

[jhbell]

Summary of Changes

This PR adds accentColor to the list of theme-supported properties under the color space. This way, the chose accent-color can be set using a color from the theme.

The Problem

Today, setting the accent color to a key in the theme does not pull the corresponding value from the theme. Our team ran into this issue recently trying to set the accent color for a checkbox element.

i.e. accentColor: 'primary' -> accentColor: 'primary'

Expected Behavior

accentColor: 'primary' -> accentColor: 'tomato' ('tomato' would be the value in the theme in this example)

Version

Published prerelease version: v0.16.2-develop.2

Changelog

:tada: This release contains work from new contributors! :tada: Thanks for all your work! :heart: Jeff Bell ([@jhbell](https://github.com/jhbell)) :heart: Paweł Kowalewski ([@pawkow](https://github.com/pawkow)) #### 🐛 Bug Fix #### 🏠 Internal - docs: Fix incorrect config sample [#2467](https://github.com/system-ui/theme-ui/pull/2467) ([@pawkow](https://github.com/pawkow)) #### Authors: 2 - Jeff Bell ([@jhbell](https://github.com/jhbell)) - Paweł Kowalewski ([@pawkow](https://github.com/pawkow))

[vercel[bot]]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Comments	Updated (UTC)
theme-ui	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jan 2, 2024 4:51pm

[codesandbox-ci[bot]]

This pull request is automatically built and testable in CodeSandbox.

To see build info of the built libraries, click here or the icon next to each commit SHA.

Latest deployment of this branch, based on commit a797834f7e75e49d52f8fd7467d7ac161710f549:

Sandbox	Source
next-theme-ui-example	Configuration
gatsby-plugin-theme-ui-example	Configuration