Adding a Custom Scrollbar to enhance UI.

## Description

I want to introduce a custom scrollbar in this website, because the default scrollbars look odd.

**Describe the solution you'd like**
A custom scrollbar.

**Describe alternatives you've considered**
A clear and concise description of any alternative solutions or features you've considered.

## Additional Information

**Context**
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**Potential Implementation** (optional)
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**Screenshots or Mockups** (optional)
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**Priority** (optional)
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**Additional Notes** (optional)
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