body{
  background-color: #abdde8;

  overflow: hidden;
  margin: 0;
  height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
}

.fixed{
  position: fixed;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

.form-demo{
  position: relative;
  
  width: 400px;
  height: 600px;
}

/* 切换按钮所在的白色区域 */
.switch{
  background-color: #FCFBFA;
  width: 100%;
  height: 140px;
  position: absolute;
  left: 0;
  bottom: 0;
  border-radius: 8px;
  text-align: center;
}

/* 切换按钮 */
#change:checked+label,
/* +用来选择同级后面最近的元素  */
#change:not(:checked)+label{
  background-color: #FFB8CE;
  color: white;
  width: 280px;
  padding: 8px 0;
  /* 用padding方便文字垂直居中 */
  font-size: 24px;
  font-weight: 600;
  position: absolute;
  bottom: 22px;
  left: 50%;
  transform: translate(-50%);
  border-radius: 8px;
  cursor: pointer;
  text-align: center;
}

/* 旋转体 */
.turn{
  width: 100%;
  height: 400px;
  position: absolute;
  top: 0;
  perspective: 800px;
  /* 旋转的时候的透视效果 */
}
.over{
  width: 100%;
  height: 100%;
  transform-style: preserve-3d;
  transition: all 1.6s ease;
  /* 旋转持续时间 */
  /* ease是慢快慢 */
}
#change:checked
~
.turn .over{
  transform: rotateY(180deg);
}
form{
  position: absolute;
  background-color: #FCFBFA;
  height: 100%;
  border-radius: 8px;
  transform-style: preserve-3d;
  text-align: center;
}
.sign{
  transform: rotateY(180deg);
}

h1, h2{
  color: #1f2029;
  user-select: none;
}
h1{
  margin-top: 38px;
  transform-style: preserve-3d;
  transform: translate3d(0, 0, 1px);
}

input{
  background-color: #4E495D;
  width: 70%;
  height: 48px;
  border-radius: 8px;
  margin-bottom: 20px;
  padding: 0 16px;
  font-size: 18px;
  color: #c4c3ca;
  font-weight: 500;
  outline: none;
  border: none;
  box-shadow: 0 4px 8px 0 rgba(78, 73, 79, .5);
  transform-style: preserve-3d;
  transform: translate3d(0, 0, 1px);
}
.login input:nth-child(-n+3){
  /* 选择class为login的子元素中的前三个input */
  margin: 20px 0;
}

.btn{
  background-color: #981E61;
  border: none;
  width: 280px;
  font-size: 24px;
  font-weight: 600;
  padding: 6px 0;
  color: white;
  border-radius: 8px;
  margin-top: 15px;
  cursor: pointer;
}