<style>
@keyframes yanipsonme {
0%, 100% { opacity: 1; }
50% { opacity: 0; }
}

.yanip-sonen-metin {
animation: yanipsonme 1s infinite;
font-size: 24px;
color: red;
}
</style>
<title>Yanıp Sönen Metin</title>
<div class="yanip-sonen-metin">Yanıp Sönen Metin</div>