<aside id="guide"></aside>

<div id="yay"></div>

<footer>
  <button id="minus">-2vmin</button><button id="plus">+2vmin</button>
  
  <p id="message">Full demo requires support for Web Animations API and `composite: 'add'`. Available in Firefox Nightly 59+ and Chrome Canary 65+ (with Experimental Web Platform Features flag enabled).</p>
  <div>
    <p><code>transform: rotate(0deg) translateX(<span id="from">0</span>vmin)</code></p>
    <p><code>transform: rotate(2880deg) translateX(<span id="to">40</span>vmin)</code></p>
  </div>
</footer>

#yay {
  border: 1vmin solid hsl(143, 55%, 55%);
  width: 5vmin;
  height: 5vmin;
}

html {
  font-size: 62.5%;
}
body {
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  overflow: hidden;
  background: hsl(231, 35%, 8%);
  font-family: system-ui, 'Segoe UI', -apple-system, sans-serif;
}
*, *::before, *::after {
  box-sizing: border-box;
}

aside {
  --guide: hsla(303, 85%, 55%, .4);
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  width: 80vmin;
  height: 2vh;
  max-height: 1.6rem;
}

aside::before, aside::after {
  content: '';
  position: absolute;
  top: 0;
  width: 40vmin;
  bottom: 0;
  z-index: 1;
}
aside::before {
  --guide: hsl(43, 85%, 55%);
  --guide-a: hsla(43, 85%, 55%, .4);
  left: 0;
  background:
    linear-gradient(to right, transparent 2.5vmin, var(--guide) 2.5vmin, var(--guide) calc(2.5vmin + .1rem), transparent calc(2.5vmin + .1rem)),
    linear-gradient(to right, transparent 7.5vmin, var(--guide) 7.5vmin, var(--guide) calc(7.5vmin + .1rem), transparent calc(7.5vmin + .1rem)),
    linear-gradient(to right, transparent 12.5vmin, var(--guide) 12.5vmin, var(--guide) calc(12.5vmin + .1rem), transparent calc(12.5vmin + .1rem)),
    linear-gradient(to right, transparent 17.5vmin, var(--guide) 17.5vmin, var(--guide) calc(17.5vmin + .1rem), transparent calc(17.5vmin + .1rem)),
    linear-gradient(to right, transparent 22.5vmin, var(--guide) 22.5vmin, var(--guide) calc(22.5vmin + .1rem), transparent calc(22.5vmin + .1rem)),
    linear-gradient(to right, transparent 27.5vmin, var(--guide) 27.5vmin, var(--guide) calc(27.5vmin + .1rem), transparent calc(27.5vmin + .1rem)),
    linear-gradient(to right, transparent 32.5vmin, var(--guide) 32.5vmin, var(--guide) calc(32.5vmin + .1rem), transparent calc(32.5vmin + .1rem)),
    linear-gradient(to right, transparent 37.5vmin, var(--guide) 37.5vmin, var(--guide) calc(37.5vmin + .1rem), transparent calc(37.5vmin + .1rem)),
    linear-gradient(to bottom, transparent 45%, var(--guide-a) 45%, var(--guide-a) 55%, transparent 55%);
}
aside::after {
  --guide: hsl(303, 85%, 55%);
  --guide-a: hsla(303, 85%, 55%, .4);
  right: 0;
  background:
    linear-gradient(to right, hsl(183, 85%, 55%) 0rem, hsl(183, 85%, 55%) .2rem, transparent .2rem),
    linear-gradient(to right, transparent 5vmin, var(--guide) 5vmin, var(--guide) calc(5vmin + .2rem), transparent calc(5vmin + .2rem)),
    linear-gradient(to right, transparent 10vmin, var(--guide) 10vmin, var(--guide) calc(10vmin + .2rem), transparent calc(10vmin + .2rem)),
    linear-gradient(to right, transparent 15vmin, var(--guide) 15vmin, var(--guide) calc(15vmin + .2rem), transparent calc(15vmin + .2rem)),
    linear-gradient(to right, transparent 20vmin, var(--guide) 20vmin, var(--guide) calc(20vmin + .2rem), transparent calc(20vmin + .2rem)),
    linear-gradient(to right, transparent 25vmin, var(--guide) 25vmin, var(--guide) calc(25vmin + .2rem), transparent calc(25vmin + .2rem)),
    linear-gradient(to right, transparent 30vmin, var(--guide) 30vmin, var(--guide) calc(30vmin + .2rem), transparent calc(30vmin + .2rem)),
    linear-gradient(to right, transparent 35vmin, var(--guide) 35vmin, var(--guide) calc(35vmin + .2rem), transparent calc(35vmin + .2rem)),
    linear-gradient(to right, transparent 0vmin, transparent calc(40vmin - .2rem), var(--guide) calc(40vmin - .2rem), var(--guide) 40vmin, transparent 40vmin),
    linear-gradient(to bottom, transparent 45%, var(--guide-a) 45%, var(--guide-a) 55%, transparent 55%);
}

footer {
  position: absolute;
  bottom: 1rem;
  font-size: 1.2rem;
  color: white;
  text-align: center;
  left: 0;
  right: 0;
  font-size: 1.2rem;
}
footer p {
  margin: .8rem 0;
  line-height: 1.35;
}
footer div {
  overflow-x: auto;
  white-space: nowrap;
}
code {
  font-size: 1.4rem;
  font-family: monospace;
}

button {
  display: none;
}
.supports-composite-add button {
  display: inline-block;
  margin: .5rem;
  padding: .6rem 1rem;
}
.supports-composite-add #message {
  display: none;
}

const yay = document.getElementById('yay');

const minusButton = document.getElementById('minus');
const plusButton = document.getElementById('plus');

if (yay.animate) {
  var animation = yay.animate([
    { transform: 'rotate(0deg) translateX(0vmin)'},
    { transform: 'rotate(2880deg) translateX(40vmin)'}
  ], {
    iterations: Infinity,
    duration: 10000,
    easing: 'ease-in-out',
    direction: 'alternate',
    composite: 'add'
  });
  
  if (animation.effect && animation.effect.composite === 'add') {
    document.documentElement.classList.add('supports-composite-add');
    
    plusButton.addEventListener('click',e => addTranslateX(delta));
    minusButton.addEventListener('click',e => addTranslateX(-delta));
  }
}

const originalRadius = 40;
let radius = originalRadius;
var delta = 2;

function addTranslateX(amount){
  radius = radius + amount;
  yay.animate([
    { transform: 'translateX(0vmin)'},
    { transform: `translateX(${amount}vmin)`}
  ], {
    iterations: 1,
    duration: 1000,
    easing: 'ease-in-out',
    fill: 'forwards',
    composite: 'add'
  });

  updateReference();
}




const guide = document.getElementById('guide');
const from = document.getElementById('from');
const to = document.getElementById('to');

function updateReference() {
  guide.animate([
    { width: `${radius * 2}vmin`}
  ], {
    iterations: 1,
    duration: 1000,
    easing: 'ease-in-out',
    fill: 'forwards'
  });

  from.textContent = radius - originalRadius;
  to.textContent = radius;
  
  if (radius <= 0) {
    minus.setAttribute('disabled', 'disabled');
  } else {
    minus.removeAttribute('disabled');
  }
}