html, body {
  --pacman: #fcec0f;
  --background: #222;
  --wall: #5558ff;
  --dot: #eee;
  --size: 8vmin;
  --halfSize: calc(var(--size) / 2);
  --negativesize: calc(var(--size) * -1);
  --positionTop: calc(50vh - var(--halfSize));
  --timing: 5s;
  --timingEat: 0.4s;
  
  background-color: var(--background);
  background-image:  linear-gradient( var(--background),  var(--background)), radial-gradient(var(--dot) 10%, transparent 0);
  background-size: 100vw var(--size), var(--size) var(--size);
  background-repeat: no-repeat, repeat;
  background-position: calc(-100vw - var(--halfSize)) var(--positionTop), 0 0;
  box-shadow: inset 0 0 0 1vmin var(--background), inset 0 0 0 1.5vmin var(--wall), inset 0 0 0 2vmin var(--background), inset 0 0 0 2.5vmin var(--wall);
  width: 100vw;
  height: 100vh;
  padding: 0;
  margin: 0;
  border-radius: 2vmin;
  overflow: hidden;
  animation: move var(--timing) linear infinite;
}

@keyframes move {
  0% { background-position: calc(-100vw - var(--halfSize)) var(--positionTop), center center; }
  100% { background-position: 0 var(--positionTop), center center; }
}


body::after {
  content: "";
  display: block;
  top: calc(var(--positionTop) + 1vmin);
  left: 0;
  position: absolute;
  width: calc(var(--size) - 2vmin);
  height: calc(var(--size) - 2vmin);
  border-radius: 50%;
  background: conic-gradient(var(--pacman) 55deg, transparent 0 125deg, var(--pacman) 0);
  animation: eat var(--timingEat) linear infinite, 
             movePacman var(--timing) linear infinite;
}

@keyframes eat {
  0%, 50% { background: conic-gradient(var(--pacman) 55deg, transparent 0 125deg, var(--pacman) 0); }
  25% { background: conic-gradient(var(--pacman) 55deg, var(--pacman) 0); }
}

@keyframes movePacman {
  0% { transform: translate(var(--negativesize), 0) }
  100% { transform: translate(100vw, 0) }
}

body::before {
  content: "";
  display: block;
  position: absolute;
  width: 3vmin;
  height: var(--size);
  background: var(--background);
  left: 0;
  box-shadow: calc(100vw - 3vmin) 0 var(--background);
  top: var(--positionTop);
}