* {
  margin: 0;
  padding: 0;
}
body {
  /**background: #333; 这句注释了就是无背景色**/
  display: flex;
  width: 100%;
  height: 100vh;
  justify-content: center;
  align-items: center;
  overflow: hidden;
}
.back {
  width: 100%;
  height: 100%;
  position: absolute;
}
.back span {
  white-space: nowrap;
}
.main {
  color: #ff7f50;
  font-size: 50px;
  text-shadow: 0 0 5px white, 0 0 10px white, 0 0 20px white;
}
#start {
  position: absolute;
  transform: translateY(80px);
  font-size: 25px;
  background: transparent;
  border: 1px solid #ff7f50;
  padding: 10px;
  border-radius: 10px;
  color: gray;
  cursor: pointer;
}
#start:hover {
  background: white;
  color: #ff7f50;
}