Added dark mode toggle button and functionality to the sign up page

[gbengaoluwadahunsi]

Summary In this contribution, I've integrated dark mode functionality into the SignUp page, providing users with the option to toggle between dark and light modes seamlessly. This enhancement aims to improve the visual experience during the SignUp process and accommodate user preferences for a darker interface.

Motivation The motivation behind this pull request is to enhance my SignUp page's usability and cater to users' diverse preferences. By introducing dark mode, I aim to reduce eye strain and enhance readability, particularly for users accessing the SignUp page in low-light environments. This feature underscores my commitment to continuously improving user experience and accessibility across my application.

Testing I conducted thorough manual testing to ensure the successful implementation of dark mode on the SignUp page. Testing involved validating the toggle's functionality across different browsers and devices to ensure a consistent user experience. By rigorously testing this feature, I aim to ensure its reliability and effectiveness in enhancing user experience.

[gbengaoluwadahunsi]

Hello@birm. I separated my pull requests as you instructed over a week ago. I, unfortunately, got to know today that I closed all my pull requests, I have reopened all now.