body {
  overflow: hidden;
  user-select: none;
}
.logo {
  margin-top: 75px;
  text-align: center;
}
.playground {
  margin: 25px auto 75px;
  width: 640px;
  position: relative;
}
.header {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 30px;
  line-height: 30px;
  font-weight: bold;
  font-size: 24px;
  color: #663366;
  z-index: 999;
}
.header .score {
  float: left;
  padding-left: 6px;
}
.header .title {
  float: right;
  padding-right: 6px;
}
canvas {
  display: block;
  background-color: #f8f7fb;
}
.back {
  width: 100px;
  height: 50px;
  margin: 0 auto;
}