.grid-demo {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 15px;
    margin: 20px 0;
}
.grid-item {
    border: 2px solid #ddd;
    border-radius: 4px;
    min-height: 80px;
    display: flex;
    align-items: center;
    justify-content: center;
}
.grid-item:empty {
    border-style: dashed;
    border-color: #ccc;
    background: #fafafa;
    opacity: 0.5;
}
.grid-item:empty::before {
    content: "Empty";
    color: #999;
    font-style: italic;
}
.grid-item:not(:empty) {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    font-weight: bold;
}