#flipsack-top-btn {
  position: fixed;
  bottom: 20px;
  right: 20px;
  width: 44px;
  height: 44px;
  /* background: #067b5a;  your brand color */
  color: #ef4939;
  /* font-size: 24px; */
  text-align: center;
  line-height: 44px;
  border-radius: 50%;
  cursor: pointer;
  box-shadow: 0 6px 18px rgba(0,0,0,0.2);
  display: none; /* initially hidden */
  z-index: 9999;
  transition: opacity 0.2s ease, transform 0.2s ease;
}
#flipsack-top-btn.show {
  display: block;
}
@media (max-width: 640px) {
  #flipsack-top-btn { width: 40px; height: 40px; font-size: 20px; line-height: 40px; }
}