<!-- this part adds a play/pause functionality to the demo, the paused state being the default for a more comfortable viewing experience -->
  <input type="checkbox" name="play" id="play">
  <label for="play" class="playBtn"></label>

  <!-- this is the main focus of this lesson -->
  <div class="scene">
    <div class="cube">
      <div class="wall horizontal"></div>
      <div class="wall horizontal"></div>
      <div class="wall vertical"></div>
      <div class="wall vertical"></div>
      <div class="wall applicate"></div>
      <div class="wall applicate"></div>
    </div>
  </div>

body {
  margin: 0; /* this overrides the default margin - which is crucial if your background isn't white/blank/undefined */
  box-sizing: border-box; /* another one of those standard overrides that you'll need to put in every darn time */
  background-color: black; /* the hex code for dark gray, the equivalent of rgb(48,48,48) or hsl(0deg 0% calc( 100% / 16 *3)), and a shorthard for #333333 )*/
  display: grid; /* you could alternately use */
  place-items: center; /* centers every object vertically and horizontally */
  min-height: 100vh; /* we need the viewport (the browser window) to be 100vh (100 viewport height units) so that there is enough space to suspend the object in */
  font-size: .5vh; /* sets a fontsize dependent on the height of the viewport */
}

.scene {
  width: 100em; /* sets the width to be 100 units of the font size, thus ensuring responsive scaling that mimics percentages */
  aspect-ratio: 1; /* makes sure the height matches the width of the container, making it a square*/
  perspective: 250em; /* sets the distance of the perspective */
  position: absolute; /* makes the position of the container independent of any other neighboring container - placed wherever you want rather than relative to its neighbors, and free to overlap */
}

.scene * {
  transform-style: preserve-3d; /* makes sure that each container nested inside the .scene tag treats its nested content as a 3D object rather than a 2D projection */
  position: absolute; /*see absove*/
  inset: 0; /* gives the containers nested in the .scene tag a margin of 0, thus making them fill it 100% in width and height; this is shorthand for top, right, bottom, left */
}

.cube {
  animation: spin 6s linear infinite; /* adds a slow spinning animation */
}

.wall:nth-child(odd) {
  --direction: 1; /* variable for the direction of the .wall transforms; this one keeps the value the same */
}

.wall:nth-child(even) {
  --direction: -1; /* variable for the direction of the .wall transforms; this one turns value to its negative */
  filter: invert(); /* inverts the colors */
}

.horizontal {
  background-color: red;
  transform: rotateY( calc( 90deg*var(--direction) ) ) translateZ(50em); /* rotate the wall left or right, depending on the variable, then go forward by 50em */
}

.vertical {
  background-color: green;
  transform: rotateX( calc( 90deg*var(--direction) ) ) translateZ(50em); /* rotate the wall up or down, depending on the variable, then go forward by 50em */
}

.applicate {
  background-color:blue;
  transform: translateZ( calc( 50em*var(--direction) ) ); /* move the wall forward - or back, depending on the variable - by 50em */
}

@keyframes spin { /* the details of the cube's spinning animation: */

  100% { /* in the course of the animation, at the end of it... */
    rotate: y 360deg; /* ...the cube will make a full 360 degree turn, adding to the the 20 degrees that it was already rotated */
  }

}


/* OPTIONAL READING

This section details the appearance and the functioning of the play/pause toggler. It is not a part of the cube - but still a fun thing to learn if you're up for it.

*/

input {
  display: none; /* hides the input, we'll have a label for it instead that is nicer than a tick-box */
}

.playBtn { /* that's the label */
  background-color: black;
  position: absolute;
  width: 40em;
  aspect-ratio: 1; /* makes sure the height matches the width of the container, making it a square*/
  z-index: 1; /* places the label on a layer above the cube - as otherwise it'd be inside the 3D solid, and you wouldn't be able to interact with it */
  display: grid; /* this label will have nested content, and we want it centered */
  place-items: center; /* all children are placed at the center of the container */
  transition: all .5s ease-in-out; /* when you interact with the button - hover, check/uncheck the input - it will change appearance. This makes it switch between each look smoothly rather than instantly */
  --dist: calc(100%/6); /* gap between the two vertical bars of the pause button */
  clip-path: polygon(0 0, 0 50%, 100% 50%, 100% 50%, 0 50%, 0 100%, 100% 50%, 100% 50%); /* cutour for the PLAY button*/
}

.playBtn:hover { /* when you mouse over the label... */
  scale: 1.25; /* ...it gets a little bit larger */
}

#play:not(:checked) ~ .scene .cube { /* if the PLAY button hasn't been pressed */
  animation-play-state: paused; /* ...the animation is paued */
}

#play:checked ~ .playBtn { /* when you hit the PLAY button */
  rotate: -90deg; /* ...it turns to its side */
  clip-path: polygon(0 0, 0 calc(50% - var(--dist)), 100% calc(50% - var(--dist)), 100% calc(50% + var(--dist)), 0 calc(50% + var(--dist)), 0 100%, 100% 100%, 100% 0);
}

@media (orientation: portrait) { /* for mobile screens displaying in portait mode (a tall, narrow rectangle) */
  body {
    font-size: .5vw; /* the font size is now depended on the viewport width - rather than height - since now it's the narrower of the two dimensions */
  }
}

// This pen is used for demonstration in my tutorial on 3D CSS cubes at https://mackfitz.hashnode.dev/css-3d-the-cube-part-2