.leftflx {
    float: left;
}

.rightflx {
    float: right;
}

.clearflx::after {
    content: "";
    display: block;
    clear: both;
}
html {
    font-size: 16px;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, 
                "Noto Sans", sans-serif, "Apple Color Emoji", "Segoe UI Emoji", 
                "Segoe UI Symbol", "Noto Color Emoji";
    margin: 0;
    padding: 0;
}
header .beijing {
    height: 100vh;
    width: 100vw;
    background-color: rgba(74,66,62, 1);
}
header .beijing nav {
    margin: 1rem;
}
header .beijing .nav {
    height: 1.3rem;
    width: 5rem;
    color: #fff;
    text-align: center;
}

header .beijing .nav:hover {
    color: rgb(18, 199, 139);
    cursor: pointer;
}
/* header .beijing .nav:active~.main-nav{
    left: 20vw;
} */
header .beijing .main-nav {
    position: fixed;
    height: 100vh;
    width: 80vw;
    background-color: #fff;
    top: 0px;
    left: 120vw;
    transition: left 1s;
}
header .beijing {
    text-align: center;
}
header .beijing .shang{
    font-size: 3rem;
    color: #fff;
    line-height: 100vh;
    letter-spacing: 1rem;
    font-weight: 900;
}