A snippet to run in any web page to highlight all elements

highlightElements.js

(function() {
	var elements = document.body.getElementsByTagName('*');
	var items = [];
	for (var i = 0; i < elements.length; i++) {
		if (elements[i].innerHTML.indexOf('* { background:#000!important;color:#0f0!important;outline:solid #f00 1px!important; background-color: rgba(255,0,0,.2) !important; }') != -1) {
			items.push(elements[i]);
		}
	}
	if (items.length > 0) {
		for (var i = 0; i < items.length; i++) {
			items[i].innerHTML = '';
		}
	} else {
		document.body.innerHTML +=
			'<style>* { background:#000!important;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; }</style>';
	}
})()