How can we make a CSS debug tool

This works quite well:

function DEBUGborders(){
   console.log("Borders on");
   var Element = document.createElement('style');
   document.head.appendChild(Element);
   var Sheet = Element.sheet;
   Sheet.insertRule("*{outline: 1px red solid;}", 0);
}

Type DEBUGborders into the console and red outlines will appear.