.spinner {
    display: none; /* 初期状態で非表示 */
    border: 4px solid #f3f3f3; /* Light grey */
    border-top: 4px solid #3498db; /* Blue */
    border-radius: 50%;
    width: 40px;
    height: 40px;
    animation: spin 1s linear infinite;
    position: fixed;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}
@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}