button.loading {
    position: relative;
    pointer-events: none;
    opacity: 0.75;
}

button.loading::before {
    content: "";
    position: absolute;
    width: 16px;
    height: 16px;
    top: 50%;
    left: 50%;
    margin-left: -8px;
    margin-top: -8px;
    border: 2px solid transparent;
    border-top-color: currentColor;
    border-radius: 50%;
    animation: spin 0.6s linear infinite;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}