Debug your styles with outline (Copy/Paste the JS in your console and press D)

debug.css

* {
  outline: 1px solid rgba(251,8,7,.24)
}

debug.js

document.onkeydown = function(event) {
  event = event || window.event;
  // Press 'D'
  if (event.target.tagName === 'BODY' && event.keyCode === 68) {
    if (document.styleSheets[0].cssRules[0].selectorText === '*') {
      document.styleSheets[0].deleteRule(0);
    } else {
      document.styleSheets[0].insertRule('* {outline: 1px solid rgba(251,8,7,.24)}', 0);
    }
  }
};