devFind bugfix: webpage theme is now consistent across page reloads

Description

Fixed the issue at #1131, where the current theme of the website is lost when you reload the page. So, if I change my theme to dark mode, it won't persist across the page reload.

Related Issues

#1131

Changes Proposed

properly implemented the useTheme hook in the sideBar component
removed the redundant and insufficient state management in the sidebar component for the theme.
fixed spelling errors
changed default theme from dark to light
moved the updating of the localStorage from toggleTheme function to the useEffect

Checklist

[x] I have read and followed the Contribution Guidelines.
[x] All new and existing tests passed.
[ ] I have updated the documentation to reflect the changes I've made.
[x] My code follows the code style of this project.
[x] The title of my pull request is a short description of the requested changes.