#spinner_container {
  position: fixed;
  top: 0;
  left: 0;
  width: 100vw;
  height: 100vh;
  background: rgba(255, 255, 255, 0.7);
  display: none; /* hidden by default */
  align-items: center;
  justify-content: center;
  z-index: 99;
  pointer-events: all; /* blocks clicks */
}

#spinner_container.active {
  display: flex;
}

.spinner {
  border: 8px solid #f3f3f3;
  border-top: 8px solid #3498db;
  border-radius: 50%;
  width: 60px;
  height: 60px;
  animation: spin 1s linear infinite;
}

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