[Feature] - Implement darkmode

[gurpreet-legend]

Currently, the chatting application does not have a dark mode.

Checkpoints:

• [ ] Make a toggle button via which users can switch to dark mode easily
• [ ] Set the dark mode as the default mode for start-up

[HammadKhaan]

@gurpreet-legend assign this issue to me, please.

[gurpreet-legend]

@HammadKhaan, go ahead!