Update the Mac Desktop slack CSS

Paint slack black.md

In the console

export SLACK_DEVELOPER_MENU=true
open /Applications/Slack.app

In slack UI

right-click on anything -> inspect element

In the Inspector console

var cssURI = 'https://gist.githubusercontent.com/tadast/5b6624f69d75667b997cd97844e159cb/raw/c1f0c7b0409bf16db49426916cd90940737b8c7f/slack%2520dark%2520scheme.css';
$.get(cssURI).then(function(css) {
   $('<style />').text(css).appendTo('body')
});