/* Generic loading spinner inside button */
.btn-submit {
  position: relative;
  overflow: hidden;
  transition: background .3s, transform .1s;
}

.btn-submit:disabled {
  opacity: .8;
  cursor: not-allowed;
}

/* Spinner */
.btn-submit.loading {
  color: transparent !important;  /* hide button text while loading */
}

.btn-submit.loading::after {
  content: "";
  position: absolute;
  top: 50%;
  left: 50%;
  width: 1.2rem;
  height: 1.2rem;
  margin-top: -0.6rem;
  margin-left: -0.6rem;
  border: 2px solid #fff;
  border-top-color: transparent;
  border-radius: 50%;
  animation: btn-spin .6s linear infinite;
}

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

/* Optional: little "press down" effect */
.btn-submit:active:not(:disabled) {
  transform: scale(0.97);
}