feat: Implement Dark Mode Toggle for Additional Web Page

[thevijayshankersharma]

Related Issue

Closes #276

Description

This pull request extends the existing dark mode functionality from the Home page to the following sections of the website: About Us, Simulations, 3D Visualisations, Quizzes, Videos, and Doubt Engine. The goal is to provide users with a consistent user experience across all sections by enabling them to switch between light and dark themes based on their preferences. This enhancement aims to improve usability and accessibility, especially in low-light environments.

Screenshots

Checklist

• [x] My code adheres to the established style guidelines of the project.
• [x] I have included comments in areas that may be difficult to understand.
• [x] My changes have not introduced any new warnings.
• [x] I have conducted a self-review of my code.