header burger {
    display: block;
    width: 30px;
    height: 22px;
    padding: 10px;
    cursor: pointer;
    
    x {
        display: block;
        width: 30px;
        height: 18px;
        position: relative;

        border-top: 2px solid #000;
        border-bottom: 2px solid #000;

        transition: border-color .3s, width .3s, height .3s, margin .3s;
    }

    x:before,
    x:after {
        content: '';
        position: absolute;
        width: 30px;
        height: 2px;
        background-color: #000;
        top: 8px;
        left: 0;

        transition: transform .3s, top .3s, left .3s;
    }
}

body.nav header burger {
    x {
        width: 0;
        height: 0;
        margin: 8px 10px;
        border-color: transparent;
    }

    x:before,
    x:after {
        top: 0;
        left: -10px;
    }

    x:before {
        transform: rotate(45deg);
    }

    x:after {
        transform: rotate(-45deg);
    }
}