bug: The toggle icon at sidebar is not working at all

[Julliet-Mohanta]

Problem: The toggle icon at sidebar is just static with a white square colour box which is not changing theme on clicking. Basically, there is no functionality of the button for now.
Proposed solution:

1. Looking and analysing the ThemeToggle.jsx file and index.css file to understand the root cause.
2. Fixing the issue to enable theme toggling.

[Julliet-Mohanta]

/assign
GSSoC'26