Just the browser compatibility issue, try it like below with meta tag
<%@page language="abap"%>
<%@extension name="htmlb" prefix="htmlb"%>
<html>
<head>
<meta http-equiv="X-UA-Compatible" content="IE=EmulateIE11">
<style>
@-moz-keyframes blinkred {
0% { background-color: red; }
50% { background-color: white; }
100% { background-color: red; }
}
@keyframes blinkred {
0% { background-color: red; }
50% { background-color: white; }
100% { background-color: red; }
}
.critical {
-webkit-animation: blinkred 1s infinite;
-moz-animation: blinkred 1s infinite;
animation: blinkred 1s infinite;
vertical-align: center;
}
</style>
</head>
<body>
<input type="text" class="critical" value="TEST"/>
</body>
</html>