.fade-in {
    opacity: 0;
    animation: fadeinanim 3s ease-out forwards;
}
@keyframes fadeinanim {
    0% {
        opacity: 0;
    }
    40% {
        opacity: 0.2;
    }
    100% {
        opacity: 1;
    }
}

body {
    font-family: "Microsoft YaHei", "Helvetica Neue", Helvetica, Arial, sans-serif;
    background-color: #282828;
    color: #fff;
}

.header {
    top: 0px;
    width: 100%;
    height: 70px;
    background-color: #303030;
    overflow: hidden;
}

.footer {
    display: flex;
    justify-content: space-between;
    width: 100%;
    height: 40px;
    background-color: #000000af;
    padding: 8px;
    overflow: hidden;
}

.h-img {
    position: relative;
    width: 600px;
    left: 55%;
    top: -180px;
    opacity: 0.5;
}

.main-title {
    font-size: 120px;
	padding-bottom: 0;
	margin-bottom: 0;
}

.video-background {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    overflow: hidden;
    z-index: -1;
}

.video-background video {
    position: absolute;
    top: 50%;
    left: 50%;
    width: 100%;
    height: 100%;
    object-fit: cover;
    transform: translate(-50%, -50%);
    scale: 1.1;
}

.video-background .overlay {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.75);
    z-index: 1;
}

.content {
    position: relative;
    z-index: 1;
    color: white;
    padding: 20px;
}

.start-btn {
    padding-top: 15%;
    padding-left: 10%;
    font-size: 36px;
}

.main-upper {
    top: 0px;
    height: 95vh;
}

.introduce {
    color: white;
}

.partl {
    display: flex;
    left: 0;
    width: 100%;
    background-color: rgb(53, 53, 53);
    height: 450px;
    margin-bottom: 10vh;
}

.partc {
    display: flex;
    justify-content: center;
    left: 0;
    width: 100%;
    background-color: rgb(53, 53, 53);
    margin-bottom: 10vh;
}

.icon-text {
    display: grid;
    grid-template-columns: 1fr;
    grid-template-rows: repeat(3, 1fr);
    grid-column-gap: 0px;
    grid-row-gap: 0px; 
    margin: 3vh;
    margin-top: 5vh;
    padding: 2vh;
    width: 30vh;
    height: 30vh;
    overflow: hidden;
}

.icon-text i{
    grid-area: 1 / 1 / 2 / 2;
    scale: 4;
    height: 1px;
    justify-self: center;
}

.icon-text h4{
    grid-area: 2 / 1 / 3 / 2;
    justify-self: center;
}

.icon-text p{
    grid-area: 3 / 1 / 4 / 2;
    justify-self: center;
    font-size: 12px;
}

.download {
    display: flex;
}

.download-box{
    display: flex;
    flex-direction: column;
    align-items: center;
    margin: 5vh;
    width: 20vh;
    height: 20vh;
    overflow: hidden;
}

.download-box img {
    width: 20vh;
    height: 12vh;
    margin-bottom: 2vh;
}