.gallery {
    width: 100%;
}

.gallery img {
    width: 30%;
    padding: 5px;
    filter: grayscale(100%);
    transition: 1s;
}

.gallery img:hover {
    filter: grayscale(0);
    transform: scale(1.1);
}

@media(min-width: 750px) {
    .gallery img {
        width: 24%;
        padding: 2px;
    }
}