fix: improve html diff style

[huang-julien]

🔗 Linked issue

❓ Type of change

Add scroll and fix the background color in the HTML diff

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/nuxt/hints/@nuxt/hints@174

commit: 335d5ef