Feature Request: Dark Theme

[IceSentry]

I'm probably not the first one to ask, but I haven't seen any issue on the subject. A dark theme would be pretty nice since most other developer tools have a dark theme.

I can make a PR if you want. I'm just not sure how you would prefer it to be implemented. Obviously, it's gonna use a state machine to keep the state of the toggle between the light and dark theme. I see you are already using styled-components so it would be pretty trivial to use the theming functionality.

[davidkpiano]

I'm reworking the visualizer and it will indeed have themes!