#loading-mask {
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, .5);
    display: flex;
    justify-content: center;
    align-items: center;
    z-index: 9999;
    opacity: 0;
    pointer-events: none;
    transition: opacity .3s;
}
#loading-mask.show {
    opacity: 1;
    pointer-events: auto;
}
.spinner {
    width: 44px;
    height: 44px;
    border: 2px solid rgba(255, 255, 255, .3);
    border-top-color: #fff;
    border-radius: 50%;
    animation: spin 1s linear infinite;
}
@keyframes spin {
    to { transform: rotate(360deg); }
}