body
  margin: 0
  
canvas
  display: block
  
button
  position: absolute
  top: 1em
  right: 1em
  background-color: rgba(0,0,0,.3)
  border: none
  color: rgba(255,255,255,.5)
  padding: 0.5em 1em
  border-radius: 4px
  cursor: pointer