codepens/morphing-circles-animationclick-to-show-mechanics/dist/style.css

* {
  box-sizing: border-box;
}
:root {
  --primary: #b3ffb9;
  --secondary: #4d4d4d;
  --size: 200;
  --speed: 1;
}
h1 {
  font-size: 1.5rem;
  position: fixed;
  bottom: 1rem;
  right: 1rem;
  opacity: 0.5;
  font-weight: bold;
}
body {
  -webkit-box-align: center;
          align-items: center;
  background: #666;
  display: -webkit-box;
  display: flex;
  -webkit-box-pack: center;
          justify-content: center;
  min-height: 100vh;
  overflow: hidden;
  margin: 0;
}
body:before {
  border-radius: 6px;
  box-shadow: 4px 4px 0 0 #111;
  content: '';
  height: calc(var(--size) * 1px);
  left: 50%;
  position: absolute;
  top: 50%;
  -webkit-transform: translate(-50%, -50%);
          transform: translate(-50%, -50%);
  width: calc(var(--size) * 1px);
}
[type='checkbox'] {
  position: fixed;
  left: 100%;
  opacity: 0;
}
label {
  position: fixed;
  height: 100vh;
  width: 100vw;
  z-index: 2;
}
:checked ~ .container {
  --speed: 5;
  --primary: rgba(179,255,185,0.5);
  --secondary: rgba(77,77,77,0.5);
  border: 4px dashed #fff;
  overflow: visible;
}
:checked ~ .container:before {
  background: #fff;
}
:checked ~ .container .circle {
  border: 4px dashed #fff;
}
.container {
  --primary-switch: var(--secondary);
  --secondary-switch: var(--primary);
  border-radius: 6px;
  height: calc(var(--size) * 1px);
  width: calc(var(--size) * 1px);
  background: var(--primary);
  position: relative;
  overflow: hidden;
  -webkit-animation: flip calc(var(--speed) * 4s) steps(1) infinite, bg calc(var(--speed) * 4s) steps(1) infinite;
          animation: flip calc(var(--speed) * 4s) steps(1) infinite, bg calc(var(--speed) * 4s) steps(1) infinite;
}
.container:before {
  border-radius: 50%;
  content: '';
  height: 10px;
  left: 50%;
  position: absolute;
  top: 50%;
  -webkit-transform: translate(-50%, -50%);
          transform: translate(-50%, -50%);
  width: 10px;
  z-index: 5;
}
.circle {
  -webkit-animation: rotate calc(var(--speed) * 1s) ease-in-out infinite alternate;
          animation: rotate calc(var(--speed) * 1s) ease-in-out infinite alternate;
  height: 100%;
  left: 0%;
  position: absolute;
  top: 40%;
  -webkit-transform-origin: 50% 0%;
          transform-origin: 50% 0%;
  width: 100%;
}
.circle:after {
  --primary-switch: var(--primary);
  --secondary-switch: var(--secondary);
  -webkit-clip-path: inset(0% 45% 90% 45% round 50% 50%);
  -webkit-animation: clip calc(var(--speed) * 1s) ease-in-out infinite alternate, bg calc(var(--speed) * 4s) steps(1) infinite;
          animation: clip calc(var(--speed) * 1s) ease-in-out infinite alternate, bg calc(var(--speed) * 4s) steps(1) infinite;
  background: var(--secondary);
  clip-path: inset(0% 45% 90% 45% round 50% 50%);
  content: '';
  height: 200%;
  left: 50%;
  position: absolute;
  top: 0%;
  -webkit-transform: translate(-50%, 0);
          transform: translate(-50%, 0);
  -webkit-transform-origin: 50% 0;
          transform-origin: 50% 0;
  width: 200%;
}
@-webkit-keyframes flip {
  25% {
    -webkit-transform: rotateY(0deg) rotateX(180deg);
            transform: rotateY(0deg) rotateX(180deg);
  }
  50% {
    -webkit-transform: rotateY(180deg) rotateX(180deg);
            transform: rotateY(180deg) rotateX(180deg);
  }
  75% {
    -webkit-transform: rotateY(180deg) rotateX(0deg);
            transform: rotateY(180deg) rotateX(0deg);
  }
}
@keyframes flip {
  25% {
    -webkit-transform: rotateY(0deg) rotateX(180deg);
            transform: rotateY(0deg) rotateX(180deg);
  }
  50% {
    -webkit-transform: rotateY(180deg) rotateX(180deg);
            transform: rotateY(180deg) rotateX(180deg);
  }
  75% {
    -webkit-transform: rotateY(180deg) rotateX(0deg);
            transform: rotateY(180deg) rotateX(0deg);
  }
}
@-webkit-keyframes rotate {
  to {
    -webkit-transform: rotate(180deg) translate(0, -10%);
            transform: rotate(180deg) translate(0, -10%);
  }
}
@keyframes rotate {
  to {
    -webkit-transform: rotate(180deg) translate(0, -10%);
            transform: rotate(180deg) translate(0, -10%);
  }
}
@-webkit-keyframes clip {
  to {
    -webkit-clip-path: inset(0 0 0 0 round 0 0);
    clip-path: inset(0 0 0 0 round 0 0);
  }
}
@keyframes clip {
  to {
    -webkit-clip-path: inset(0 0 0 0 round 0 0);
    clip-path: inset(0 0 0 0 round 0 0);
  }
}
@-webkit-keyframes bg {
  25% {
    background: var(--primary-switch);
  }
  75% {
    background: var(--secondary-switch);
  }
}
@keyframes bg {
  25% {
    background: var(--primary-switch);
  }
  75% {
    background: var(--secondary-switch);
  }
}