#arrow {
    top: 25%; /* change this value to place the menu higher or lower */
    left:0;
    position: fixed;
    z-index: 100;
}

.show, .hiden {
    /* we specify the transition length for hiding and showing */
    transition: margin-left .4s ease-in;
    -webkit-transition: margin-left .4s ease-in;
}

.hiden {
    margin-left: -100px;
}

.show {
    margin-left: 0;
}

#arrow{
    cursor: pointer;
}