<!DOCTYPE html>
<html>
<head>
<style type='text/css'>
@-webkit-keyframes blink {from , to { border-color:transparent}
50%{border-color:black}
}
@-moz-keyframes blink {from , to { border-color:transparent}
50%{border-color:black}}
body {
width: 100px;
height: 100px;
border-left: 10px solid black;
-webkit-animation: 1s blink step-end infinite;
-moz-animation: 1s blink step-end infinite;
}
</style>
</head>
<body>
</body>
</html>