Added base styling accordions (+ removed red test border)

[verlev]

Pull Request

What changed?

• removed red testing border on h2:has(+ .wp-block-latest-posts__list)
• added/fixed base CSS styling for details summary block:
  • display: list-item (normalize.less added a faulty display:block to the summary element)
  • made the 'summary' title bold (cannot target only the summary within the block editor, using bold makes the whold detail summary block bold)
  • added indent + margin bottom to details summary (consistent with ul styling)

Why did it change?

• red border was a local testing left-over (excuse me..)
• accordions didn't appear to function (no base styling made them look broken)

Did you fix any specific issues?

Fixes #24

CERTIFICATION

By opening this pull request, I do agree to abide by the Code of Conduct and be bound by the terms of the Contribution Guidelines in effect on the date and time of my contribution as proven by the revision information in GitHub.

[verlev]

(please do tell me whenever I am doing/did something wrong; think it's my 1st PR to a public project; I'm used to be a solo-worker therefore this is a tad outside my comfort zone..)