Adding a theme toggle

Switches between light mode and dark mode with the default theme being light mode.

docusaurus.config.js

@@ -85,6 +85,11 @@ const config = {
           },
         ],
       },
+        colorMode: {
+        defaultMode: "light",
+        disableSwitch: false,
+        respectPrefersColorScheme: false,
+      },
     }),
 
   plugins: [