.success-modal {
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,.55);
  z-index: 9999;
  align-items: center;
  justify-content: center;
  opacity: 0;
  pointer-events: none;
  transition: display .3s ease;
}
.success-modal.is-visible {
  opacity: 1;
  pointer-events: all;
}
.success-modal:not(.is-visible) {
  display: none;
}
.success-modal.is-visible {
  display: flex;
}
.success-modal__box {
  background: #fff;
  padding: 48px 40px;
  max-width: 420px;
  width: 90%;
  text-align: center;
  box-shadow: 0 8px 40px rgba(0,0,0,.18);
  transform: translateY(16px);
  transition: transform .3s ease;
}
.success-modal.is-visible .success-modal__box {
  transform: translateY(0);
}
.success-modal__btn {
  background: var(--accent);
  color: #fff;
  border: none;
  padding: 10px 32px;
  font-size: 1rem;
  cursor: pointer;
}
.success-modal__btn:hover { background: var(--accent-hover); }