* {
    box-sizing: border-box;
}

body {
    margin: 21px;
    background: lavender;
}

h1 {
    text-align: center;
    margin-bottom: 12px;
}

.intro {
    text-align: center;
    margin-bottom: 20px;
}

.gridgallery {
    display: grid;
    grid-template-columns: 1fr;
    gap: 12px;
}

.griditem {
    background: white;
    padding: 12px;
    border: 2px solid lightgray;
    border-radius: 6px;
}

.griditem img {
    width: 100%;
    height: auto;
    display: block;
    margin-bottom: 8px;
}

@media (min-width: 600px) {
    .gridgallery {
        grid-template-columns: 1fr 1fr;
    }
}

@media (min-width: 900px) {
    .gridgallery {
        grid-template-columns: 1fr 1fr 1fr;
    }
}