#backToTopBtn {
  position: fixed;
  bottom: 40px;
  right: 40px;
  background: linear-gradient(135deg, #092c5c 75%, #ffd966 100%);
  color: #fff;
  border: none;
  border-radius: 50%;
  width: 54px;
  height: 54px;
  font-size: 2.2rem;
  box-shadow: 0 8px 28px rgba(9,44,92,0.16);
  cursor: pointer;
  opacity: 0;
  visibility: hidden;
  transition: opacity 0.42s, box-shadow 0.3s, background 0.3s;
  z-index: 99;
  display: flex;
  align-items: center;
  justify-content: center;
  outline: none;
}
#backToTopBtn.show {
  opacity: 1;
  visibility: visible;
}
#backToTopBtn:hover,
#backToTopBtn:focus {
  background: linear-gradient(135deg, #ffd966 85%, #092c5c 100%);
  color: #092c5c;
  box-shadow: 0 12px 34px #ffcc0040;
}
.backtotop-arrow {
  display: inline-block;
  font-size: 2.1rem;
  font-weight: bold;
  transition: transform 0.32s cubic-bezier(.4,1.8,.65,1.25);
}
#backToTopBtn:hover .backtotop-arrow {
  transform: translateY(-6px) scale(1.13);
}
@media (max-width:600px){
  #backToTopBtn {
    bottom: 16px; right: 16px; width: 38px; height: 38px; font-size: 1.1rem;
  }
}