*{
    margin: 0;
    padding: 0;
}
#contenedor{
    position: relative;
    width: 100%;
}
.glider{
    overflow: hidden;
}
.glider img{
    width: 100%;
    display: block;
}
.next, .prev{
    position: absolute;
    display: block;
    width: 40px;
    height: 40px;
    border: none;
    top: calc(50% - 40px);
    cursor: pointer;
    line-height: 40px;
    opacity: 20%;
    background: #FFF;
}
.next:hover, .prev:hover{
    opacity: 50%;
}
.prev{
    left: 0px;
}
.next{
    right: 0px;
}