static/css/style.css

.loader {
  border: 6px solid #1e293b;
  border-top: 6px solid #3b82f6;
  border-radius: 50%;
  width: 40px;
  height: 40px;
  animation: spin 1s linear infinite;
  margin: 20px auto;
}

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