Fix broken links and MathJax script issue

[mdapena]

Initial Checks

• The code compiles successfully without any errors or warnings.
• I have personally tested these changes on my local environment.
• I have ensured that relevant documentation has been added or updated.
• I adhere to the project structure and code standards defined in the documentation.
• My code follows the established coding style guidelines.
• I have added tests for the new code (if applicable).
• All existing tests have passed successfully.

Description

This pull request fixes broken links in the announcement banner by updating them to use the base_url, resolves an issue with the MathJax script not being found, and corrects the icons for the light/dark mode switch.