Here’s a fun one. How might we create a set of those cool Russian(Matryoshka) dolls where they nest inside one another… but in CSS?

I toyed with this idea in my head for a little while. Then, I saw a tweet from CSS-Tricks and the article image had the dolls. I took that as a sign! It was time to put fingers to the keyboard.

Our goal here is to make these fun and interactive, where we can click on a doll to open it up and reveal another, smaller doll. Oh, and stick with just CSS for the functionality. And while we’re at it, let’s replace the dolls with our own character, say a CodePen bear. Something like this:

We won’t dwell on making things pretty to start. Let’s get some markup on the page and thrash out the mechanics first.

We can’t have an infinite amount of dolls. When we reach the innermost doll, it’d be nice to be able to reset the dolls without having to do a page refresh. A neat trick for this is to wrap our scene in an HTML form. That way we can use an input and set the type attribute to reset to avoid using any JavaScript.

<form>
  <input type="reset" id="reset"/>
  <label for="reset" title="Reset">Reset</label>
</form>

Next, we need some dolls. Or bears. Or something to start with. The key here will be to use the classic checkbox hack and any associated form labels. As a note, I’m going to use Pug to handle the markup because it supports loops, making things a little easier. But, you can certainly write the HTML by hand. Here’s the start with form fields and labels that set up the checkbox hack.

Try clicking some of the inputs and hitting the Reset input. They all become unchecked. Nice, we’ll use that.

We have some interactivity but nothing is really happening yet. Here’s the plan:

1.We’ll only show one checkbox at a time
2.Checking a checkbox should reveal the label for the next checkbox.
3.When we get to the last checkbox, there our only option should be to reset the form.

The trick will be to make use of the CSS adjacent sibling combinator (+).

input:checked + label + input + label {
  display: block;
}

When a checkbox is checked, we need to show the label for the next doll, which will be three siblings along in the DOM. How do we make the first label visible? Give it an explicit display: block via inline styles in our markup. Putting this together, we have something along these lines:

Clicking each label reveals the next. Hold on, the last label isn’t shown! That’s correct. And that’s because the last label doesn’t have a checkbox. We need to add a rule that caters to that last label.

input:checked + label + input + label,
input:checked + label + label {
  display: block;
}

Cool. We’re getting somewhere. That’s the basic mechanics. Now things are going to get a little trickier.

Basic styling

You might be thinking, “Why aren’t we hiding the checked label?” Good question! But, if we hide it straight away, we won’t have any transition between the current doll and the next. Before we start animating our dolls, let’s create basic boxes that will represent a doll. We can style them up so they mimic the doll outline without the detail.

.doll {
  color: #fff;
  cursor: pointer;
  height: 200px;
  font-size: 2rem;
  left: 50%;
  position: absolute;
  text-align: center;
  top: 50%;
  transform: translate(-50%, -50%);
  width: 100px;
}

.doll:nth-of-type(even) {
  background: #00f;
}

.doll:nth-of-type(odd) {
  background: #f00;
}

Clicking one doll instantly reveals the next one and, when we’ve reached the last doll, we can reset the form to start again. That’s what we want here.

The mechanics

We are going to animate the dolls based on a center point. Our animation will consist of many steps:

1. Slide the current doll out to the left.
2. Open the doll to reveal the next one.
3. Move the next doll where the current one started.
4. Make the current doll fade out.
5. Assign the next doll as the current doll.

Let’s start by sliding the current doll out to the left. We apply an animation when we click a label. Using the :checked pseudo-selector we can target the current doll. At this point, it’s worth noting that we are going to use CSS variables to control animation speed and behavior. This will make it easier to chain animations on the labels.

:root {
  --speed: 0.25;
  --base-slide: 100;
  --slide-distance: 60;
}

input:checked + label {
  animation: slideLeft calc(var(--speed) * 1s) forwards;
}

@keyframes slideLeft {
  to {
    transform: translate(calc((var(--base-slide) * -1px) + var(--slide-distance) * -1%), 0);
  }
}

That looks great. But there’s an issue. As soon as we click a label, we could click it again and reset the animation. We don’t want that to happen.

How can we get around this? We can remove pointer events from a label once it’s been clicked.

input:checked + label {
  animation: slideLeft calc(var(--speed) * 1s) forwards;
  pointer-events: none;
}

Great! Now once we have started, we can’t stop the animation chain from happening.

Next up, we need to crack open the doll to reveal the next one. This is where things get tricky because we are going to need some extra elements, not only to create the effect that the doll is opening up, but also to reveal the next doll inside of it. That’s right: we need to duplicate the inner doll. The trick here is to reveal a “fake” doll that we swap for the real one once we’ve animated it. This also means delaying the reveal of the next label.

Now our markup updates labels so that they contain span elements.

<label class="doll" for="doll--1">
  <span class="doll doll--dummy"></span>
  <span class="doll__half doll__half--top">Top</span>
  <span class="doll__half doll__half--bottom">Bottom</span>
</label>

These will act as the “dummy” doll as well as the lid and base for the current doll.

.doll {
  color: #fff;
  cursor: pointer;
  height: 200px;
  font-size: 2rem;
  position: absolute;
  text-align: center;
  width: 100px;
}

.doll:nth-of-type(even) {
  --bg: #00f;
  --dummy-bg: #f00;
}

.doll:nth-of-type(odd) {
  --bg: #f00;
  --dummy-bg: #00f;
}

.doll__half {
  background: var(--bg);
  position: absolute;
  width: 100%;
  height: 50%;
  left: 0;
}

.doll__half--top {
  top: 0;
}

.doll__half--bottom {
  bottom: 0;
}

.doll__dummy {
  background: var(--dummy-bg);
  height: 100%;
  width: 100%;
  position: absolute;
  top: 0;
  left: 0;
}

The lid requires three translations to create the opening effect: one to pop it up, one to move it left, and then one to pop it down.

@keyframes open {
  0% {
    transform: translate(0, 0);
  }
  33.333333333333336% {
    transform: translate(0, -100%);
  }
  66.66666666666667% {
    transform: translate(-100%, -100%);
  }
  100% {
    transform: translate(-100%, 100%);
  }
}

Next is where we can use CSS custom properties to handle changing values. Once the doll has slid over to the left, we can open it. But how do we know how long to delay it from opening until that happens? We can use the --speed custom property we defined earlier to calculate the correct delay.

It looks a little quick if we use the --speed value as it is, so let’s multiply it by two seconds:

input:checked + .doll {
  animation: slideLeft calc(var(--speed) * 1s) forwards;
  pointer-events: none;
}

input:checked + .doll .doll__half--top {
  animation: open calc(var(--speed) * 2s) calc(var(--speed) * 1s) forwards; // highlight
}

Much better:

Now we need to move the inner “dummy” doll to the new position. This animation is like the open animation in that it consists of three stages. Again, that’s one to move up, one to move right, and one to set down. It’s like the slide animation, too. We are going to use CSS custom properties to determine the distance that the doll moves.

:root {
  // Introduce a new variable that defines how high the dummy doll should pop out.
  --pop-height: 60;
}

@keyframes move {
  0% {
    transform: translate(0, 0) translate(0, 0);
  }
  33.333333333333336% {
    transform: translate(0, calc(var(--pop-height) * -1%)) translate(0, 0);
  }
  66.66666666666667% {
    transform: translate(0, calc(var(--pop-height) * -1%)) translate(calc((var(--base-slide) * 1px) + var(--slide-distance) * 1%), 0);
  }
  100% {
    transform: translate(0, calc(var(--pop-height) * -1%)) translate(calc((var(--base-slide) * 1px) + var(--slide-distance) * 1%), calc(var(--pop-height) * 1%));
  }
}

Almost there!

The only thing is that the next doll is available as soon as we click a doll. that means we can spam click our way through the set.

Technically, the next doll shouldn’t show until the “fake” one has moved into place. It’s only once the “fake” doll is in place that we can hide it and reveal the real one. That means we going to use zero-second scale animations! That’s right. We can play pretend by delaying two zero-second animations and using animation-fill-mode.

@keyframes appear {
  from {
    transform: scale(0);
  }
}

We actually only need one set of @keyframes. because we can re-use what we have to create the opposite movement with animation-direction: reverse. With that in mind, all our animations get applied something like this:

// The next doll
input:checked + .doll + input + .doll,
// The last doll (doesn't have an input)
input:checked + .doll + .doll {
  animation: appear 0s calc(var(--speed) * 5s) both;
  display: block;
}

// The current doll
input:checked + .doll,
// The current doll that isn't the first. Specificity prevails
input:checked + .doll + input:checked + .doll {
  animation: slideLeft calc(var(--speed) * 1s) forwards;
  pointer-events: none;
}

input:checked + .doll .doll__half--top,
input:checked + .doll + input:checked + .doll .doll__half--top {
  animation: open calc(var(--speed) * 2s) calc(var(--speed) * 1s) forwards;
}

input:checked + .doll .doll__dummy,
input:checked + .doll + input:checked + .doll .doll__dummy {
  animation: move calc(var(--speed) * 2s) calc(var(--speed) * 3s) forwards, appear 0s calc(var(--speed) * 5s) reverse forwards;
}

Note how important the variables are, especially where we are chaining animations. That gets us almost where we need to be.

I can hear it now: “They’re all the same size!” Yep. That’s the missing piece. They need to scale down. The trick here is to adjust the markup again and make use of CSS custom properties yet again.

<input id="doll--0" type="checkbox"/>
<label class="doll" for="doll--0" style="display: block; --doll-index: 0;">
  <span class="doll__dummy-container">
    <span class="doll__dummy"></span>
  </span> //highlight
  <span class="doll__container">
    <span class="doll__half doll__half--top"></span>
    <span class="doll__half doll__half--bottom"></span>
  </span>
</label> 

We introduced a CSS custom property inline that tells us the index of the doll. We can use this to generate a scale of each half as well as the fake inner doll. The halves will have to scale to match the actual doll size, but the fake inner doll scale will need to match that of the next doll. Tricky!

We can apply these scales inside the containers so that our animations are not affected.

:root {
  --scale-step: 0.05;
}

.doll__container,
.doll__dummy-container {
  height: 100%;
  left: 0;
  position: absolute;
  top: 0;
  width: 100%;
}

.doll__container {
  transform: scale(calc(1 - ((var(--doll-index)) * var(--scale-step))));
  transform-origin: bottom;
}

.doll__dummy {
  height: 100%;
  left: 0;
  position: absolute;
  top: 0;
  transform: scale(calc(1 - ((var(--doll-index) + 1) * var(--scale-step))));
  transform-origin: bottom center;
  width: 100%;
} 

Note how the .doll__dummy class uses var(--doll-index) + 1) to calculate the scale so that it matches the next doll. 👍

Lastly, we re-assign the animation to the .doll__dummy-container class instead of the .doll__dummy class.

input:checked + .doll .doll__dummy-container,
input:checked + .doll + input:checked + .doll .doll__dummy-container {
  animation: move calc(var(--speed) * 2s) calc(var(--speed) * 3s) forwards, appear 0s calc(var(--speed) * 5s) reverse forwards;
}

Here’s a demo where the containers have been given a background color to see what’s happening.

We can see that, although the content size changes, they remain the same size. This makes for consistent animation behavior and makes the code easier to maintain.

Finishing touches

Wow, things are looking pretty slick! All we need are some finishing touches and we are done!

The scene starts to look cluttered because we’re stacking the “old” dolls off to the side when a new one is introduced. So let’s slide a doll out of view when the next one is revealed to clean that mess up.

@keyframes slideOut {
  from {
    transform: translate(calc((var(--base-slide) * -1px) + var(--slide-distance) * -1%), 0);
  }
  to {
    opacity: 0;
    transform: translate(calc((var(--base-slide) * -1px) + var(--slide-distance) * -2%), 0);
  }
}

input:checked + .doll,
input:checked + .doll + input:checked + .doll {
  animation: slideLeft calc(var(--speed) * 1s) forwards,
    slideOut calc(var(--speed) * 1s) calc(var(--speed) * 6s) forwards;
  pointer-events: none;
}

The new slideOut animation fades the doll out while it translates to the left. Perfect. 👍

That’s it for the CSS trickery we need to make this effect work. All that’s left style the dolls and the scene.

We have many options to style the dolls. We could use a background image, CSS illustration, SVG, or what have you. We could even throw together some emoji dolls that use random inline hues!

Let’s go with inline SVG.

I’m using the same underlying mechanics we’ve already covered. The difference is that I’m also generating inline variables for hue and lightness so the bears sport different shirt colors.

There we have it! Stacking dolls — err, bears — with nothing but HTML and CSS! All the code for all the steps is available in this CodePen collection.

As always, I'd love to hear what you have to say. Leave a comment or come find me on Twitter!