* {
  padding: 0;
  margin: 0;
}

.shell {
  width: 100%;
  position: relative;
  padding: 80px 0;
  transition: 0.3s ease 0s;
  background-attachment: fixed;
  background-size: cover;
  align-items: center; 
  text-align: center;
  justify-content: flex-start;
}

.shell::before {
  position: absolute;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
  background: rgba(99, 99, 99, .8);
  content: "";
 }

.header {
  width: 100%;
  text-align: center;
  margin-bottom: 80px;
  position: relative;
  align-items: center;
}

.title {
  color: #fff;
  font-size: 46px;
  font-weight: normal;
  margin: 0;
}

.timeline {
  display: flex;
  margin: 0 auto;
  flex-wrap: wrap;
  flex-direction: column;
  max-width: 700px;
  position: relative;
}

.content-title {
  font-weight: normal;
  font-size: 66px;
  margin: -10px 0 0 0;
  transition: 0.4s;
  padding: 0 10px;
  box-sizing: border-box;
  color: #fff;
}

.content-desc {
  margin: 0;
  font-size: 15px;
  box-sizing: border-box;
  color: rgba(255, 255, 255, .7);
  line-height: 25px;
}
/* 中间线的样式 */
.timeline::before {
  position: absolute;
  left: 50%;
  width: 2px;
  height: 100%;
  margin-left: -1px;
  content: "";
  background: rgba(255, 255, 255, .07);
}

.item {
  padding: 40px 0;
  opacity: 0.3;
  filter: blur(2px);
  transition: 0.5s;
  box-sizing: border-box;
  width: calc(50% - 40px);
  display: flex;
  position: relative;
  transform: translateY(-80px);
}

.item::before {
  content: attr(data-text);
  letter-spacing: 3px;
  width: 100%;
  position: absolute;
  color: rgba(255, 255, 255, .5);
  font-size: 13px;
  border-left: 1px solid rgba(255, 255, 255, .5);
  top: 70%;
  margin-top: -5px;
  padding-left: 15px;
  opacity: 0;
  right: calc(-100% - 56px);
  font: 900 20px '';
  letter-spacing: 5px;
}

.item:nth-child(even) {
  align-self: flex-end;
}

.item:nth-child(even)::before {
  right: auto;
  text-align: right;
  left: calc(-100% - 56px);
  padding-left: 0;
  border-left: 2px solid rgba(255, 255, 255, .5);
  padding-right: 15px;
}

.item--active {
  opacity: 1;
  transform: translateY(0);
  filter: blur(0px);
}

.item--active::before {
  top: 50%;
  transition: 0.3s all 0.2s;
  opacity: 1;
}

.item--active .content-title {
  margin: -50px 0 20px 0;
}
.img {
  max-width: 100%;
  box-shadow: 0 10px 15px rgba(0, 0, 0, .4);
}

.subtitle {
  color: rgba(255, 255, 255, .5);
  font-size: 1rem;
  letter-spacing: 5px;
  margin: 10px 0 0 0;
  font-weight: normal;
}

.footer {
  padding: 95px 0;
  text-align: center;
}

.footer a {
  color: #999;
  display: inline-block;
}

@media only screen and (max-width: 767px) {
  .item {
    align-self: baseline !important;
    width: 100%;
    padding: 0 30px 150px 80px;
  }

  .item::before {
    left: 10px !important;
    padding: 0 !important;
    top: 50px;
    text-align: center !important;
    width: 60px;
    border: none !important;
  }

  .item:last-child {
    padding-bottom: 40px;
  }
}

@media only screen and (max-width: 767px) {
  .timeline::before {
    left: 40px;
  }
}