save the theme(light and dark theme) in localstorage

**Is your feature request related to a problem? Please describe.**
saving theme will enhance user experience as it will not change on every reload as it is right now.

**Describe the solution you'd like**
Saving it in localstorage.

**Describe alternatives you've considered**
none.

**Additional context**
none.

please assign me this under SWOC.