Added dark mode functionality to the website

[Premonvitha-Sai]

Fixes Issue🛠️

Closes #515

Description👨‍💻

I have implemented dark mode functionality and added feature-specific icons for each page.

Type of Change📄

• New feature (non-breaking change which adds functionality)

Checklist✅

• I am an Open Source contributor
• I have performed a self-review of my code
• My code follows the style guidelines of this project
• I have commented on my code, particularly in hard-to-understand areas

Screenshots/GIF📷

[github-actions]

Hey @Premonvitha-Sai, Welcome to the project CalcDiverse! 🎊
Thanks for your contribution! Your effort makes this project better. Keep it up! 🙌
Please wait for the PR to be reviewed. Happy Coding!! ✨

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[Nihal4777]

@Premonvitha-Sai You should take latest Pull of the code and resolve conflicts.

[Premonvitha-Sai]

@Nihal4777 can you tell me clearly how to do it?
Because I don't know how to do it.