body {
  background: #333;
  font-family: 'Source Sans Pro', sans-serif;
  display: flex;
  flex-flow: column nowrap;
  justify-content: center;
  align-items: center;
  min-width: 700px;
 }

canvas {
  background-color: #999;
}

.explain {
  color: white;
  font-size: 18px;
  margin: 20px;    
  line-height: 26px;
  width: 90%;
}

button {
  width: 200px;
  height: 40px;
  margin: 20px;
  font-size: 20px;
}