[docs] Fix Colors > Contrast docs page

[cee-chen]

Summary

closes #7500

The text color broke in #7298, as part of this changelog item:

• Fixed EuiListGroupItem to pass style props to the wrapping <li> element alongside className and css. All other props will be passed to the underlying content.

The contrast page was passing style to EuiListGroupItem and relying it to go onto the <button> element instead of the <li>. This broken the inherited color styling of the various button(s).

While here I also noticed a whole lot of other things going wrong with this page (😅) and pushed up several fixes - see the commit history.

QA

• https://eui.elastic.co/pr_7506/#/theming/colors/contrast looks correct/non-broken compared to production

General checklist

• Browser QA
  - [ ] Checked in mobile
  - [ ] Checked for accessibility including keyboard-only and screenreader modes
  • Checked in both light and dark modes
  • Checked in Chrome, Safari, Edge, and Firefox
• Docs site QA - See QA steps
• Code quality checklist - N/A
• Release checklist - N/A, docs only
• Designer checklist - N/A

[kibanamachine]

Preview staging links for this PR:

• Docs site: https://eui.elastic.co/pr_7506/
• Storybook: https://eui.elastic.co/pr_7506/storybook

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: a4943ec

History

• 💚 Build #1357 succeeded eb644ae
• 💔 Build #1355 failed a06ec83

[tkajtoch]

LGTM 🚢