Must include Font Awesome (here: https://fortawesome.github.io/Font-Awesome/get-started/) for icons to show up 

.slick-prev,
.slick-next {
    font-size: 0;
    position: absolute;
    bottom: 20px;
    color: #d5122f;
    border: 0;
    background: none;
    z-index: 1;
}

.slick-prev {
    left: 20px;
}

    .slick-prev:before {
        content: "\f137";
        font: 40px/1 'FontAwesome';
        color: #337ab7;
    }

.slick-next {
    right: 20px;
    text-align: right;
}

    .slick-next:before {
        content: "\f138";
        font: 40px/1 'FontAwesome';
        color: #337ab7;
    }

    .slick-prev:hover:after,
    .slick-next:hover:after {
        color: #7e7e7e;
    }