body {
  margin: 0;
  padding: 0;
  background: #fff;
  font-family: monospace;
  text-align: center;
}

.screen {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  height: 100vh;
}

.hidden {
  display: none;
}

canvas {
  background: #fff;
  display: block;
  margin: auto;
  width: 100vw;
  height: 100vh;
}

.button {
  width: 80px;
  margin: 10px;
  cursor: pointer;
}

.control {
  width: 80px;
  position: fixed;
  bottom: 20px;
}

#btnLeft { left: 20px; }
#btnRight { right: 20px; }

.music-btn {
  position: fixed;
  top: 10px;
  right: 10px;
  width: 50px;
}
.music-btn.off { opacity: 0.4; }

#score-box {
  position: fixed;
  top: 10px;
  left: 10px;
  background: #fff;
  border: 3px solid #000;
  padding: 5px 10px;
  font-size: 20px;
}