[bug] Light/Dark icon in different size

**Describe the bug**
When toggling between the light mode and the dark mode, the icon of the dark mode is rendered large as size which disturbs the styling of the entire navbar.

**To Reproduce**
Steps to reproduce the behaviour:
1. Go to `https://akshitagupta15june.github.io/PetMe/index.html`
2. Click on the `Dark mode` icon in the top right corner.
3. See the error

**Expected behavior**
Both the icon should be equal in size.

**Screenshots**

https://github.com/akshitagupta15june/PetMe/assets/97666287/a0d9bd63-1ddb-441e-ae04-793dc4ad8ee6

**Additional context**

Shall I work on this issue? I'm in `GSSOC'23`