[fix/docs]: Improve announcement banner color and style

[anuptiwari17]

What has changed?

This PR improves the announcement banner color and style in the Keploy docs website:

• The banner now uses the theme’s primary color instead of plain white, making it consistent with the rest of the documentation style.
• Minor layout improvements for better alignment and visibility.

This PR resolves #3002.

Type of change

• [x] Bug fix (non-breaking change which fixes an issue).

How Has This Been Tested?

• Ran npm run build → No errors.
• Ran npm run serve → Verified that the announcement banner shows the updated styling as intended.
• Screenshot:

Checklist

• [x] My code follows the style guidelines of this project.
• [x] I have performed a self-review of my own code.