* {
    padding: 0;
    margin: 0;
}

.shell {
    width: 100%;
    position: relative;
    padding: 80px 0;
    background-attachment: fixed;
    background-size: cover;
}

.shell:before {
    position: absolute;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    background: rgba(99, 99, 99, 0.8);
    content: "";
}

.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, 0.7);
    line-height: 25px;
}

.timeline:before {
    position: absolute;
    left: 50%;
    width: 2px;
    height: 100%;
    margin-left: -1px;
    content: "";
    background: rgba(255, 255, 255, 0.07);
}

.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 {
    /* 设置在伪元素before中的内容  */
    content: attr(data-text);
    letter-spacing: 3px;
    width: 100%;
    position: absolute;
    color: rgba(255, 255, 255, 0.5);
    font-size: 13px;
    border-left: 2px solid rgba(255, 255, 255, 0.5);
    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: none;
    border-right: 2px solid rgba(255, 255, 255, 0.5);
    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, 0.4);
}

.subtitle {
    color: rgba(255, 255, 255, 0.5);
    font-size: 16px;
    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;
    }
}