Add a Night Toggle Button

Add a button that lets you toggle between Night Mode and the current color scheme.
Also, make sure the toggle button is not too big and distracting, it should be a small icon in the top right.

For more, you may refer to:
https://www.w3schools.com/howto/howto_js_toggle_dark_mode.asp
https://www.w3schools.com/howto/howto_css_switch.asp