Styled governance banner and inner card container.

[fairlighteth]

Summary

• Styles the governance banner between light/dark mode.
• Replaces the inner card containers with a different color.

[github-actions[bot]]

• 🔭 GP Swap: CoW Protocol v2 Swap UI

[W3stside]

Yeah let's merge this asap

[elena-zh]

Looks nice!