I've been working on a dark mode skin for the Indigo website and it's in decent enough shape to share. In order to use it, an intermediate browser extension is required--I prefer the Cascadea extension for Safari. Cascadea injects custom css (cascading style sheets) into web pages before the pages are displayed. The skin itself changes nothing except the page's display properties. I have no affiliation with the Cascadea extension, but I do recommend it. That said, any browser extension that injects css should work. The custom css file itself can be found on GitHub. This is completely unofficial and Matt and Jay have nothing to do with it.
Here's a couple examples: