Added a theme changing button in NavBar#85

sufiyan-siddiqui233 wants to merge 2 commits intonumcys:mainnumcys/Basic_website_HTML_CSS_only:mainfrom

sufiyan-siddiqui233:Sufiyansufiyan-siddiqui233/Basic_website_HTML_CSS_only:SufiyanCopy head branch name to clipboard