scss mixin for dark theme management

[gihanrangana]

Description

A new SCSS snippet was added under the layouts category. which is helpful to change styles for dark theme

Type of Change

• ✨ New snippet
• 🛠 Improvement to an existing snippet
• 🐞 Bug fix
• 📖 Documentation update
• 🔧 Other (please describe):

Checklist

• I have tested my code and verified it works as expected.
• My code follows the style and contribution guidelines of this project.
• Comments are added where necessary for clarity.
• Documentation has been updated (if applicable).
• There are no new warnings or errors from my changes.

Related Issues

Closes #

Additional Context

This is the working demo for this snippet
https://stackblitz.com/edit/react-hook-usedarkmode

Screenshots (Optional)

Click to view screenshots

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[Mathys-Gasnier]

Hey, we recently updated how snippets are stored, please update your PR to match the changes, you will be able to see how to add snippets in CONTRIBUTING.md.
For ref: #87