CSS image slider carousel with cross fade - how to get timing right?

Question

I am trying to create an image carousel using CSS where each image appears for four seconds, then cross fades to the next image. I want to include three images that loop.

I found code on another post that seemed close to what I needed, but it was for five images. I thought it would be easy to edit it to just feature three, but I'm not familiar enough with animation timing in CSS and made a mess of it. Now it shows the three images but doesn't show each long enough, and the fade-out / fade-in animations aren't overlapping, leaving a gap between each image.

.crossfade>figure {
  animation: imageAnimation 12s linear infinite 0s;
  backface-visibility: hidden;
  background-size: cover;
  background-position: center center;
  color: transparent;
  height: 100%;
  left: 0px;
  opacity: 0;
  position: absolute;
  top: 0px;
  width: 100%;
  z-index: 0;
}

.crossfade {
  height: 450px;
  width: 100%;
}

.crossfade>figure:nth-child(1) {
  background-image: url('https://picsum.photos/id/237/200/300');
}

.crossfade>figure:nth-child(2) {
  animation-delay: 4s;
  background-image: url('https://picsum.photos/seed/picsum/200/300');
}

.crossfade>figure:nth-child(3) {
  animation-delay: 8s;
  background-image: url('https://picsum.photos/200/300?grayscale');
}

@keyframes imageAnimation {
  0% {
    animation-timing-function: ease-in;
    opacity: 0;
  }
  8% {
    animation-timing-function: ease-out;
    opacity: 1;
  }
  17% {
    opacity: 1
  }
  25% {
    opacity: 0
  }
  100% {
    opacity: 0
  }
}

<div class="crossfade">
  <figure></figure>
  <figure></figure>
  <figure></figure>
</div>

Answer 1

You need to update the percentages. Something like this:

@keyframes imageAnimation {
  0% {
    animation-timing-function: ease-in;
    opacity: 0;
  }
  10% { 
    animation-timing-function: ease-out;
    opacity: 1;
  }
  33% {
    opacity: 1;
  }
  66% {
    opacity: 0;
  }
}

Answer 2

It looks like a case of just tweaking the timing for animation in the .crossfade>figure selector, as well as the animation-delay in each image.

Here's a snippet below, it seems like 2s per image seems to be enough. With an additional 2s for the overall loop.
Hence: animation: imageAnimation 8s linear infinite 0s;

.crossfade>figure {
  animation: imageAnimation 8s linear infinite 0s;
  backface-visibility: hidden;
  background-size: cover;
  background-position: center center;
  color: transparent;
  height: 100%;
  left: 0px;
  opacity: 0;
  position: absolute;
  top: 0px;
  width: 100%;
  z-index: 0;
}

.crossfade {
  height: 450px;
  width: 100%;
}

.crossfade>figure:nth-child(1) {
  background-image: url('https://picsum.photos/id/237/200/300');
}

.crossfade>figure:nth-child(2) {
  animation-delay: 2s;
  background-image: url('https://picsum.photos/seed/picsum/200/300');
}

.crossfade>figure:nth-child(3) {
  animation-delay: 4s;
  background-image: url('https://picsum.photos/200/300');
}

@keyframes imageAnimation {
  0% {
animation-timing-function: ease-in;
opacity: 0;
  }
  15% {
opacity: 1;
  }
  50% {
animation-timing-function: ease-out;
opacity: 1;
  }
  75% {
opacity: 1
  }
  90% {
opacity: 0
  }
  100% {
opacity: 0
  }
}

<div class="crossfade">
  <figure></figure>
  <figure></figure>
  <figure></figure>
</div>

Additionally, I've gone a step further here, if you were generating the images with JavaScript (let's say you were getting the images from an endpoint). You could use a custom variable var(--n) to specifiy the delay like so:

.crossfade>figure {
  animation-delay: calc(var(--n) * 2s);
}

This would still give you the number same delay time per image.

.crossfade>figure {
  animation: imageAnimation 8s linear infinite 0s;
  backface-visibility: hidden;
  background-size: cover;
  background-position: center center;
  color: transparent;
  height: 100%;
  left: 0px;
  opacity: 0;
  position: absolute;
  top: 0px;
  width: 100%;
  z-index: 0;
}

.crossfade {
  height: 450px;
  width: 100%;
}

.crossfade>figure {
  animation-delay: calc(var(--n) * 2s);
}

@keyframes imageAnimation {
  0% {
animation-timing-function: ease-in;
opacity: 0;
  }
  15% {
opacity: 1;
  }
  50% {
animation-timing-function: ease-out;
opacity: 1;
  }
  75% {
opacity: 1
  }
  90% {
opacity: 0
  }
  100% {
opacity: 0
  }
}

<div class="crossfade">
  <figure style="--n: 0; background-image: url('https://picsum.photos/id/237/200/300');"></figure>
  <figure style="--n: 1; background-image: url('https://picsum.photos/seed/picsum/200/300');"></figure>
  <figure style="--n: 2; background-image: url('https://picsum.photos/200/300');"></figure>
</div>

If you went even further and had a variable number of images returned from an endpoint.

You could calculate (on .crossfade>figure) animation-duration: calc(calc(--l * 2s) + 2s) where --l were the number of images to cycle through.

See the snippet above to see how --n were passed in, and you could apply the same technique to pass a value for --l.