test.js

javascript: (function() {
  let domStyle = document.getElementById('domStylee');
  if (domStyle) {
    document.body.removeChild(domStyle);
    return;
  }
  domStyle = document.createElement("style");
  domStyle.setAttribute('id', 'domStylee');
  domStyle.append(
    ['* { color:#0f0!important;outline:solid #f00 1px!important; background-color: rgba(255,0,0,.2) !important; }'],
    ['* * { background-color: rgba(0,255,0,.2) !important; }'],
    ['* * * { background-color: rgba(0,0,255,.2) !important; }'],
    ['* * * * { background-color: rgba(255,0,255,.2) !important; }'],
    ['* * * * * { background-color: rgba(0,255,255,.2) !important; }'],
    ['* * * * * * { background-color: rgba(255,255,0,.2) !important; }'],
    ['* * * * * * * { background-color: rgba(255,0,0,.2) !important; }'],
    ['* * * * * * * * { background-color: rgba(0,255,0,.2) !important; }'],
    ['* * * * * * * * * { background-color: rgba(0,0,255,.2) !important; }'].join()
  );
  document.body.appendChild(domStyle);
})();