#btn-download-invoice,
#btn-send-invoice,
#project-success,
#user-success
{
    margin: 0 10px; 
    padding: 20px; 
    border-radius: 10px;
}
#button-container{
    display: flex; 
    justify-content: center; 
    align-items: center;
}

.loader {
    display: none;
    position: fixed;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(255, 255, 255, 0.8);
    z-index: 9999;
}

.loader:before {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    width: 60px;
    height: 60px;
    margin: -30px 0 0 -30px;
    border: 6px solid #f3f3f3;
    border-top: 6px solid #3498db;
    border-radius: 50%;
    animation: spin 1s linear infinite;
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}