css-layout-hack.js

// create a bookmark and use this code as the URL, you can now toggle the css on/off
// thanks+credit: https://dev.to/gajus/my-favorite-css-hack-32g3
javascript: (function() {
	var styleEl = document.getElementById('css-layout-hack');
	if (styleEl) {
		styleEl.remove();
		return;
	}
	styleEl = document.createElement('style');
	styleEl.id = 'css-layout-hack';
	styleEl.innerHTML = '* { 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; }';
	document.body.append(styleEl);
})();

awesome, thank for that tip