body {
    overflow: auto;
}

.header {
    background: #49b4ff;
}
.img-gallery {
    width: 80%;
    padding-top: 10%;
    padding-bottom: 5%;
    margin: auto;
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(min(100%/2, max(64px, 100%/4)), 1fr));
    grid-gap: 15px;
    align-self: center;
}

.img-gallery img{
    width: 100%;
    height: 100%;
    cursor: pointer;
    filter: grayscale(.75);
    transition: .75s ease-in-out;
    align-self: space-evenly;
}

.img-gallery img:hover {
    filter: grayscale(0);
}