.trail {
  position: absolute;
  border-radius: 50%;
  background: red;
  transition: all 3s;
}

#game {
  position: relative;
  width: 800px;
  height: 300px;
  border: 1px solid;
  overflow: hidden;
}

body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
}