Check out example codes for "fade in css". It will help you in understanding the concepts better.

Code Example 1

<style>
.fade-in {
  animation: fadeIn ease 10s;
  -webkit-animation: fadeIn ease 10s;
  -moz-animation: fadeIn ease 10s;
  -o-animation: fadeIn ease 10s;
  -ms-animation: fadeIn ease 10s;
}
@keyframes fadeIn {
  0% {
    opacity:0;
  }
  100% {
    opacity:1;
  }
}

@-moz-keyframes fadeIn {
  0% {
    opacity:0;
  }
  100% {
    opacity:1;
  }
}

@-webkit-keyframes fadeIn {
  0% {
    opacity:0;
  }
  100% {
    opacity:1;
  }
}

@-o-keyframes fadeIn {
  0% {
    opacity:0;
  }
  100% {
    opacity:1;
  }
}

@-ms-keyframes fadeIn {
  0% {
    opacity:0;
  }
  100% {
    opacity:1;
}
</style>
<div class="fade-in">
   <img src="../images/epic-cat-picture.png">
</div>

Code Example 2

/* Just add .fade-in class to element */

.fade-in {
	animation: fadeIn 2s;
  	opacity: 1;
}

@keyframes fadeIn {
  from {
  	opacity: 0;
  }
  to {
 	opacity: 1;
  }
}

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