.book {
    padding: 15px 0 0;
    margin: auto
}

.shelf {
    border-bottom: 30px solid #a5a5a5;
    border-left: 20px solid transparent;
    border-right: 20px solid transparent;
    top: -20px;
    z-index: auto;/*-10;*/
    margin-bottom: 50px
}

    .shelf:after {
        content: '';
        background: url(../img/concrete_bg_dark.jpg) top left repeat-x #686868;
        height: 20px;
        width: calc(100% + 40px);
        position: absolute;
        top: 30px;
        left: 0;
        right: 0;
        z-index: 1;
        margin: 0 -20px
    }