body
{
	background-color: #4444ee;	
}

@keyframes blaat
{
    0%   {margin-left: 0%; opacity: 0.1;}
	25%  {opacity: 1;}
    50%  {margin-left: 95%; opacity: 0.1;}
	75%  {opacity: 1;}
    100% {margin-left: 0%; opacity: 0.1;}
}

#blokje
{
	width: 5%;
	height: 2rem;
	background-color: red;
	margin-top: 25%;
	margin-left: 0%;
	opacity: 0.1;
	animation-name: blaat;
    animation-duration: 4s;
	animation-iteration-count: infinite;
}