@import url('https://fonts.googleapis.com/css?family=Poppins:200,300,400,500,600,700,800,900&display=swap');
*
{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Poppins',sans-serif;
}
:root
{
    --black:#333;
    --white:#fff;
    --default:linear-gradient(to right bottom, #4868dc, #5276e1, #5e83e5, #6a90e8, #789deb, #72aaf3, #6eb7f9, #6dc3fe, #54d3ff, #42e1ff, #46effc, #5ffbf1);
    --buton: #845EC2;
}
.dark
{
    --black:#fff;
    --white:#333;
    --default:linear-gradient(to right bottom, #333333, #363636, #3a3a3a, #3d3d3d, #414141, #434343, #464646, #484848, #4a4a4a, #4b4b4b, #4d4d4d, #4f4f4f);
}
header
{
    position: absolute;
    display: flex;
    justify-content: space-between;
    align-items: center;
    width: 100%;
    padding: 40px 100px;
    z-index: 10000;
}
header .logo
{
    position: relative;
    background: ;
    display: inline-flex;
    color: var(--black);
    text-decoration: none;
    font-size: 2em;
    font-weight: 700;
    letter-spacing: 0.05em;
    text-transform: uppercase;
}
.righSide
{
    display: flex;
}
.btns
{
    position: relative;
    width: 20px;                /*icon宽度 根据自己需要调节*/
    height: 20px;               /*icon高度 根据自己需要调节*/
    background: ;               /*这里不设置背景 icon就不会有背景*/
    display: flex;
    justify-content: center;
    align-items: center;
    cursor: pointer;
    margin-left: 10px;  /*这是让btns div 左侧间隔10px*/
}
.btns ion-icon
{
    font-size: 1.5em;
    color: var(--black); /*--black是root中已经预设好的颜色*/
}
.btns.menuToggle ion-icon
{
    font-size: 3em;
}
.btns ion-icon:nth-child(2)
{
    display: none;  /*隐藏第二个icon*/
}
/*当 btns 后面有active 第二个图标 显示*/
.btns.active ion-icon:nth-child(2)
{
    display: block;
}
/*当 btns 后面有active 第一个图标 隐藏*/
.btns.active ion-icon:nth-child(1)
{
    display: none;
}
.main
{
    position: relative;
    width: 100%;
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
}
.main video
{
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    object-fit: cover;
}
.mask
{
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: 2;
    user-select: none;
    mix-blend-mode: screen;
}
.dark .mask
{
    filter: invert(1);
    mix-blend-mode: multiply;
}
.main h2
{
    position: relative;
    z-index: 3;
    font-size: 8vw;
    color: white;
    text-shadow: 0 20px 30px rgba(0,0,0,0.2);
}
.navigation
{
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    display: flex;
    justify-content: center;
    align-items: center;
    flex-direction: column;
    background-image: var(--default);
    z-index: 4;
    transition: 0.5s;
}
.navigation li
{
    list-style: none;
}
.navigation li a
{
    display: inline-flex;
    margin: 5px 0;
    font-size: 1.35em;
    text-decoration: none;
    color: var(--black);
    padding: 5px 20px;
    border-radius: 30px;
}
.navigation li a:hover
{
    background: var(--buton);
    color: var(--white);
}
.navigation.active
{
    left: 0;
}
.copyrighttext
{
    position: absolute;
    left: initial;
    bottom: 20px;
    z-index: 5;
    font-weight: 600;
    font-size: 9px;
    color: var(--black);
}
.sci
{
    position: absolute;
    right: 100px;
    bottom: 40px;
    z-index: 5;
    display: flex;
    flex-direction: column;
}
.sci li
{
    list-style: none;
}
.sci li a
{
    text-decoration: none;
    color: var(--black);
    font-size: 1.5em;
}
@media (max-width: 768px)
{
    header
    {
        padding: 20px;
    }
    .copyrighttext
    {
        left: 20px;
        bottom: 1%;
    }
    .sci
    {
        right: 20px;
        bottom: 30px;
    }
    .navigation
    {
        height: 100%;
    }
}