CSS - Hamburger menu icon with CSS

Question

<!--HTML-->
<button type="button" class="btn hamburger">
    <span>Menu</span>
    <span class="hamburger-bar">
        <span></span>
        <span></span>
        <span></span>
    </span>
</button>

<!--CSS (SCSS)-->
.hamburger {
    float: right;
    width: 100px;
    padding: 0px;
    color: #fff;
    text-decoration: none;
    text-transform: uppercase;
    background-color: transparent;
    border: 0;
    font-size: 14px;
    display: -webkit-box;
    display: -ms-flexbox;
    display: flex;
    -webkit-box-pack: center;
    -ms-flex-pack: center;
    justify-content: center;
    -webkit-box-align: center;
    -ms-flex-align: center;
    align-items: center;
    -webkit-box-orient: vertical;
    -webkit-box-direction: normal;
    -ms-flex-direction: column;
    flex-direction: column;
    -webkit-box-pack: justify;
    -ms-flex-pack: justify;
    justify-content: space-between;
    -webkit-box-orient: horizontal;
    -webkit-box-direction: normal;
    -ms-flex-direction: row;
    flex-direction: row;
    .hamburger-bar {
        margin-left: 20px;
        width: 30px;
        height: 20px;
        position: relative;
        span {
            position: absolute;
            left: 0;
            width: 100%;
            height: 1px;
            background: #fff;
            &:first-child {
                top: 0;
            }
            &:nth-child(2) {
                top: 50%;
            }
            &:last-child {
                bottom: 0;
            }
        }
    }
}