Added a custom scrollbar matching the colour theme of website

[Eshller]

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Description 📜

Added a custom Scrollbar to the website to make it look more aesthetic.

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Domain of Contribution 📊

• [x] Single page website
• [x] Animation design
• [x] Scrollbar

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Checklist ✅

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• [x] I have performed a self-review of my own code or work.
• [x] I have commented my code, particularly in hard-to-understand areas.
• [x] My changes generates no new warnings.
• [x] I'm Hacktoberfest contributor

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Screenshots / Gif (Compulsory) 📸

Before

After

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