Animated hamburger icon for mobile

header.html

<header>
  <div class="nav-toggle">
    <span></span>
    <span></span>
    <span></span>
    <span></span>
  </div>
</header>

style.css

#nav-icon3 {
    left: 15px;
    position: absolute;
    z-index: 14;

    width: 19px;
    height: 23px;
    margin: 16px auto 0;
    .lib-rotate(0deg);
    -webkit-transition: transfrom .5s ease-in-out;
    -moz-transition: transfrom .5s ease-in-out;
    -o-transition: transfrom .5s ease-in-out;
    transition: transfrom .5s ease-in-out;
    cursor: pointer;
}
#nav-icon3 span {
    display: block;
    position: absolute;
    height: 1px;
    width: 100%;
    border-bottom: 1px solid;
    border-color: inherit;
    opacity: 1;
    left: 0;
    .lib-rotate(0deg);
    -webkit-transition: .25s transform ease-in-out;
    -moz-transition: .25s transform ease-in-out;
    -o-transition: .25s transform ease-in-out;
    transition: .25s transform ease-in-out;
}
#nav-icon3 span:nth-child(1) {
    top: 0px;
}
#nav-icon3 span:nth-child(2),#nav-icon3 span:nth-child(3) {
    top: 8px;
}
#nav-icon3 span:nth-child(4) {
    top: 16px;
}

.nav-open { #nav-icon3 span:nth-child(1) {
        top: 8px;
        width: 0%;
        left: 50%;
    }}

    .nav-open { #nav-icon3 span:nth-child(2) {
        .lib-rotate(45deg);
    }}

    .nav-open {
        #nav-icon3 span:nth-child(3) {
            .lib-rotate(-45deg);
        }
    }

    .nav-open {
        #nav-icon3 span:nth-child(4) {
            top: 8px;
            width: 0%;
            left: 50%;
        }
    }