fix: make resource type code blocks theme-aware in dark mode

[nicolejms]

Fixes #340

Problem

On a resource type detail page (for example, Radius.Core/environments), code samples used a fixed light background but inherited their foreground color from the active theme. In dark mode this produced near-white text on a near-white background.

The page also used fixed GitHub colors for surrounding tables, links, borders, and status text, which did not adapt to Backstage branded themes and could provide insufficient contrast on Material-UI Paper surfaces.

Fix

• Code blocks and inline code now set explicit, matched foreground and background colors for light and dark mode.
• The copy control, including its border, hover state, and URL-encoded SVG icon, follows the code-surface palette.
• Non-code UI uses Backstage semantic theme tokens for paper backgrounds, primary and secondary text, links, dividers, and hover states.
• Required markers use the theme's primary text color rather than low-contrast red text.
• The unused codeSnippetContainer style block was removed.

Tests

The ResourceTypeDetailPage suite now has 34 passing tests, including regression coverage that:

• verifies overview code foreground and background in light and dark mode;
• verifies copy-control colors in both themes;
• renders fenced code inside a table property description and checks the JSS-computed colors; and
• supplies a custom branded palette and verifies surrounding page elements use its semantic tokens.

Validation completed with yarn tsc, yarn lint:all, yarn format:check, the focused 34-test suite, and the Impeccable UI detector.

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None

[nithyatsu]

Approving — the fix is correct and well-scoped. The <pre> now sets both background and foreground (with <code> inheriting on a transparent background), light-mode values are unchanged so it's a true no-op for the existing theme, and every hardcoded hex in the file now routes through the single getThemeColors token set. Nice catch threading the icon fill through clipboardIconUrl(fill) — the url-encoded SVG would otherwise have stayed dark-gray on dark.

Three non-blocking suggestions inline: hardcoded GitHub hexes vs. Backstage theme tokens, some dead code that could be deleted rather than refactored, and a gap in what the new tests cover. None need to block the merge.

[nithyatsu]

Thanks for the follow-up — all three earlier suggestions are addressed. The page now takes its non-code colors from the Backstage theme, the GitHub palette is limited to code blocks and the copy button, the unused style block is gone, and RT-31–34 cover the copy button, code blocks inside property descriptions, and a custom theme. LGTM.