.overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 200vh;
    background-color: rgba(0, 0, 0, 0.6);
    display: none;
    z-index: 999999999;
    align-items: center;
    text-align: center;
    justify-content: center;
}
.loader {
    border: 10px solid #f3f3f3;
    border-top: 10px solid #3498db;
    border-radius: 50%;
    width: 60px;
    height: 60px;
    animation: spin 2s linear infinite;
    position: fixed;
    top: calc(50% - 60px);
}
@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}
.overlay.loading {
    display: flex;
    align-items: center;
    text-align: center;
}