body {
  background: #f3f4f6;
}
.hidden {
  display: none;
}
.btn-loading {
  pointer-events: none;
}
.btn-loader {
  display: inline-block;
  width: 16px;
  height: 16px;
  margin-left: 8px;
  border: 2px solid currentColor;
  border-right-color: transparent;
  border-radius: 999px;
  animation: btn-spin 0.8s linear infinite;
  vertical-align: middle;
}
@keyframes btn-spin {
  to {
    transform: rotate(360deg);
  }
}