Feature request: Change to dark theme/night mode automatically based on user preference

[squeak9]

Is your feature request related to a problem? Please describe.
I just realized today that cyberchef has dark theme support , I'm kinda used to apps just selecting the theme based on your device and/or browser theme preferences so I never realized that there's a theme setting in the options.

A lot of people are probably like me, they use this tool in the dark and don't visit the options and they get this bright website. Spare their eyes and implement this.

Describe the solution you'd like
Implement this:
https://developer.mozilla.org/en-US/docs/Web/CSS/@media/prefers-color-scheme
It's supported by all the browsers.
https://caniuse.com/prefers-color-scheme

Describe alternatives you've considered
There's also this but its experimental and not supported by all browsers:
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Sec-CH-Prefers-Color-Scheme
https://caniuse.com/mdn-http_headers_sec-ch-prefers-color-scheme

Additional context
None

[aaryansr26]

I can do a little bit of research and try to implement this feature in my fork. @squeak9