Add dark mode. #32
Description
There is currently a button to switch themes, and when the button is clicked, dark mode is applied not only to the <iframe> but also to the top-level <html>.
Therefore, supporting dark mode is simple. --> https://tailwindcss.com/docs/dark-mode
Currently, the parts that need to support dark mode are mainly the navsidebar provided on the compare page and the navigation bar for the <iframe>.