h1:before{
content: 'Original Text';
font-size: 600%;
animation-name: head;
animation-duration: 4s;
animation-iteration-count: infinite;
}
@keyframes head {
0% {font-size:600%; opacity:1;}
25% {font-size:570%; opacity:0;}
50% {font-size:600%; opacity:1;}
65% {font-size:570%; opacity:0;}
80% {font-size:600%; opacity:1; content: "Changed Text"}
90% {font-size:570%; opacity:0;}
100% {font-size:600%;opacity:1; content: "Original Text"}
}