.thumbnail {
    position: relative;
    -webkit-box-shadow: none;
    box-shadow: none;
    -webkit-transition: .5s;
    /* ...and now for the proper property */
    transition: .5s;
}

.thumbnail:hover {
    -webkit-box-shadow: 0px 10px 0px 0px rgba(171, 255, 92, 1);
    box-shadow: 0px 10px 0px 0px rgba(171, 255, 92, 1);
}

.thumbnail img {
    width: 100%;
    max-width: 100%;
    display: block;
}

.descriptionbackground {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.8);
    opacity: 0;
    -webkit-transition: .5s;
    /* ...and now for the proper property */
    transition: .5s;
}

.thumbnail:hover .descriptionbackground {
    opacity: 100;
}

.imagedescription {
    color: white;
    position: absolute;
    bottom: -100px;
    width: 100%;
    text-align: center;
    -webkit-transition: .5s;
    /* ...and now for the proper property */
    transition: .5s;
    visibility: hidden;
}

.thumbnail:hover .imagedescription {
    bottom: 0;
    visibility: visible;
}

.imagedescriptionheading {
    font-family: "Istok Web";
    font-weight: 400;
    font-size: 24px;
    margin-bottom: 0;
}

.imagedescriptiontext {}