docs: change primary color from blue to indigo

[shenxianpeng]

Summary

Unify the MkDocs primary color with the cpp-linter.github.io hub site.

• Changed primary: blue → primary: indigo across all three palette modes
• Indigo matches the cpp-linter organization logo and brand identity
• The extra.css already uses #4051b5 (indigo) for mobile nav — now palette matches

Summary by CodeRabbit

• Style
  • Updated the documentation theme primary color from blue to indigo across automatic, light, and dark modes for improved visual consistency.
  • Removed a custom header/background color override to align header appearance with the new theme palette.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 6fca8dc4-7e5c-47b1-90a3-bf38a6a31302

📥 Commits

Reviewing files that changed from the base of the PR and between d4c6afc and 8514a5b.

📒 Files selected for processing (1)

• docs/stylesheets/extra.css

💤 Files with no reviewable changes (1)

• docs/stylesheets/extra.css

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Walkthrough

Updated the MkDocs Material theme primary palette color from blue to indigo for automatic, light, and dark modes, and removed a custom header/drawer background-color rule from docs/stylesheets/extra.css.

Changes

Theme Palette & Styles

Layer / File(s)	Summary
Primary color and header background removal mkdocs.yml, docs/stylesheets/extra.css	Theme primary palette changed from blue to indigo in automatic, light, and dark modes; deleted the .md-header, .md-nav--primary .md-nav__title[for="__drawer"] { background-color: #4051b5; } rule.

🎯 2 (Simple) | ⏱️ ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately and concisely describes the main change: updating the primary color from blue to indigo in the MkDocs documentation configuration.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/unify-color-indigo

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[2bndy5]

The extra.css already uses #4051b5 (indigo) for mobile nav — now palette matches

So, why not remove this CSS rule?

cpp-linter-action/docs/stylesheets/extra.css

Lines 5 to 8 in 39f903b

	.md-header,
	.md-nav--primary .md-nav__title[for="__drawer"] {
	background-color: #4051b5;
	}

IIRC, I made the primary color different from the indigo used in the header/nav because the indigo color made link text hard to read in dark mode:

on main:

after this patch:

But if that's what you want, then I'm ok with it.

[shenxianpeng]

Thanks for pointing that out. I've removed the CSS rule since the palette already handles it now.

For the dark mode concern, I checked the rendered result after the change and the indigo links still look readable to me. They're easy to distinguish from the surrounding text, so I think we're OK there.

I'd prefer to keep the colors aligned with the cpp-linter hub site for consistency.