.thumbnail {
    position: relative;
    padding: 2px 5px;
}
.caption {
    position: absolute;
    top: 60%;
    left: 0;
  /*   width:100%; */
    margin:30px;
}
.filtro-de-imagem {
    /*filter: grayscale(80%);*/
    filter: brightness(40%);
    -webkit-filter: brightness(40%);
    -moz-filter: brightness(40%);
    -ms-filter: brightness(40%);
    -o-filter: brightness(40%);
}