body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 50px;
    background: #f5f5f5;
}

main {
    display: block;
    padding: 50px;
}

h1 {
    text-align: center;
}

.grid {
    max-width: 1200px;
    margin: 0 auto;
}

.grid:after {
    content: '';
    display: block;
    clear: both;
}

.grid-item {
    width: 30%;
    margin: 10px;
    float: left;
}

.grid-item img {
    width: 100%;
    display: block;
    border-radius: 8px;
}

@media (max-width: 900px) {
    .grid-item {
        width: 45%;
    }
}

@media (max-width: 500px) {
    .grid-item {
        width: 100%;
    }
}