[UI] Add dark mode on contribution to open source

[Elaa257]

Description

Added dark mode on page contribution to open source.

Category

• [ ] Resource Addition
• [ ] Documentation
• [ ] Codebase
• [x] User Interface
• [ ] Feature Addition

Related Issue

Fixes #522

Checklist

• [x] I have followed the CONTRIBUTING guide
• [x] The name of the resource is spelled correctly (if applicable)
• [x] The link to the resource is working (if applicable)
• [x] The resource is added in the correct format (if applicable)
• [x] I have tested changes on my local computer (if applicable)

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