CSS3 Animation - Smooth Infinite Animation - html

Question

I've made a small Image animation where images changes opacity over time.It works smoothly but when last image gets to 100% it jumps straight to 0% without any transition.
I have already tried animation-direction: alternate for third image and delay for all image but it does not work for me. Delay works only first step of animation cycle after it delay becomes 0 for all.
Here is my CSS
.rightside .img-container img.first {
animation-name: first-image;
animation-duration: 9s;
animation-fill-mode: both;
animation-iteration-count: infinite;
/* animation-delay: -10s; */
}
.rightside .img-container img.second {
position: absolute;
top: 0;
animation-name: second-image;
animation-duration: 9s;
animation-fill-mode: both;
animation-iteration-count: infinite;
}
.rightside .img-container img.third {
position: absolute;
top: 0;
animation-name: final-image;
animation-duration: 9s;
animation-fill-mode: both;
animation-iteration-count: infinite;
animation-timing-function: linear;
/* animation-direction: alternate; */
}
#keyframes first-image {
0% {
opacity: 0;
}
33.3% {
opacity: 1;
}
67% {
opacity: 0;
}
100% {
opacity: 0;
}
}
#keyframes second-image {
0% {
opacity: 0;
}
33.3% {
opacity: 0;
}
67% {
opacity: 1;
}
100% {
opacity: 0;
}
}
#keyframes final-image {
0% {
opacity: 0;
}
33.3% {
opacity: 0;
}
67% {
opacity: 0;
}
100% {
opacity: 1;
}
}
HTML
<div class="img-container">
<img src="Images/Apple.png" class="first turn" alt="Image Here" />
<img src="Images/Bee.png" class="second" alt="Image Here" />
<img src="Images/Cat.png" class="third" alt="Image Here" />
</div>

Answer 1

The clasical aproach to this would be just using different delays:
div {
animation-name: all;
animation-duration: 9s;
animation-iteration-count: infinite;
width: 100px;
height: 100px;
background-color: yellow;
}
.first {
animation-delay: -3s;
background-color: lightgreen;
}
.third {
animation-delay: -6s;
background-color: lightblue;
}
#keyframes all {
0% {
opacity: 0;
}
33.3% {
opacity: 1;
}
67% {
opacity: 0;
}
100% {
opacity: 0;
}
}
<div class="first"></div>
<div class="second"></div>
<div class="third"></div>