Rambox allows having separate application for messaging services, which actually is a simplified version of Chrome. The drawback here is lack of extensions, namely Stylish and CareYourEyes because some services provide dark theme out of the box, like GMail, but Slack or Telegram doesn’t have it. Let’s see how this could be improved.

One of the biggest differences between Franz and Rambox is customizability of Rambox - it allows running custom JS code per service. With such cool feature you can apply custom CSS per service (styles could be taken from userstyles.org) using Custom Code feature of Rambox.

To use it simply grab CSS from userstyles.org, remove @-moz-document wrapper, paste CSS in following snippet and put it in Custom Code field in service’s advanced settings:

function applycss(css){
    var head = document.getElementsByTagName('head')[0];
    var s = document.createElement('style');
    s.setAttribute('type', 'text/css');
    s.appendChild(document.createTextNode(css));
    head.appendChild(s);
 }
applycss(`
// css goes here
`);