html {
    font-size: 16px;
}

@media screen and (min-width: 375px) {
    html {
        /* iPhone6的375px尺寸作为16px基准，414px正好18px大小, 600 20px */
        font-size: calc(100% + 2 * (100vw - 375px) / 39);
        font-size: calc(16px + 2 * (100vw - 375px) / 39);
    }
}
@media screen and (min-width: 414px) {
    html {
        /* 414px-1000px每100像素宽字体增加1px(18px-22px) */
        font-size: calc(112.5% + 4 * (100vw - 414px) / 586);
        font-size: calc(18px + 4 * (100vw - 414px) / 586);
    }
}
@media screen and (min-width: 600px) {
    html {
        /* 600px-1000px每100像素宽字体增加1px(20px-24px) */
        font-size: calc(125% + 4 * (100vw - 600px) / 400);
        font-size: calc(20px + 4 * (100vw - 600px) / 400);
    }
}
@media screen and (min-width: 1000px) {
    html {
        font-size: 22px;
    }
}

header {
    max-width: 768px;
    background-color: rgba(2, 8, 19, 0.3);
}

header .logo {
    width: 15%;
}

header .download {
    width: 40%;
}

@media screen and (min-width: 768px) {
    header .download {
        width: 20%;
    }
}

main {
    max-width: 768px;
}

.banner {
    background-image: url('../images/bg_01.jpg');
    background-repeat: no-repeat;
    background-size: cover;
    background-position: center;
    padding-top: 235px;
    padding-bottom: 235px;
}

.banner .slogan {
    margin-top: 5rem;
}

.banner .download-container {
    margin-top: 5rem;
}

.about-us {
    background-image: url('../images/bg_02.jpg');
    background-repeat: no-repeat;
    background-size: cover;
    background-position: center;
}

@media screen and (min-width: 576px) {
    .about-us p {
        font-size: 1.5rem;
    }
}

.about-us .video-container {
    background-image: url('../images/video_static.png');
    background-repeat: no-repeat;
    background-size: contain;
    background-position: center;
    padding: 12vw 1.1vw;
}


/* .about-us .embed-responsive-16by9::before {
    background-image: url('../images/ld_02_video_bg.png');
    background-repeat: no-repeat;
    background-size: contain;
    background-position: center;

} */

.about-us .embed-responsive-16by9::after {
    display: block;
    content: "";
    background-image: url('../images/video_btn.png');
    background-repeat: no-repeat;
    background-size: contain;
    background-position: center;
    position: absolute;
    width: 50px;
    height: 50px;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}

.about-us .hide.embed-responsive-16by9::after { 
    display: none;
}
.footer {
    background-color: rgba(2, 8, 19, 1);
    color: #fff;
}