body {
  margin: 0;
  padding: 0;
}

section {
  position: relative;
  width: 100%;
  height: 625px;
  background-size: cover;
  /* 核心：背景固定不滚动，fixed容器会重叠，滚动条下拉如果到达另一个fixed容器，会替换重叠的背景 */
  background-attachment: fixed;
  background-repeat: no-repeat;
}

.section1 {
  background-image: url(../assets/1.jpg);
}

.section2 {
  background-image: url(../assets/2.jpg);
}

.section3 {
  background-image: url(../assets/3.jpg);
}

.section4 {
  background-image: url(../assets/4.jpg);
}