Fix Slack web client high contrast colors

fix_slack.js

/* Run the following in your developer console */
(function restyle_slack() {
  let css_body = `
    .p-channel_sidebar {
      background-color: #222222 !important;
    }

    #team_menu {
      background-color: #222222 !important;
      border-bottom-color: #222222 !important;
    }

    .p-channel_sidebar__jumper {
      background-color: #333333 !important;
    }

    .p-channel_sidebar__link:hover,           
    a.p-channel_sidebar__channel:hover {
      background-color: #333333 !important;
    }
  `
  
  let css = document.createElement('style')
  css.type = 'text/css'
  css.innerText = css_body
  
  document.body.appendChild(css)
})()