Make website's viewport scroolbar dark

[reuixiy]

Hi there,

I'm reading Remix Docs and found the scroolbar is so bright...

This can be easily fixed by adding color-scheme HTML meta tag or CSS property, see https://web.dev/color-scheme/

Before

After

P.S. I can't find website's repository and issues seems not a correct place so I just put this feedback here...

[matmilbury]

@kentcdodds we're waiting for the website repo to be open sourced too. A simple PR in this case would be ideal...