.burger {
  display: inline-block;
  cursor: pointer;
  z-index: 1000;
}

.burger span {
  display: block;
  width: 30px;
  height: 3px;
  background: #333;
  margin: 6px 0;
  transition: transform 0.3s cubic-bezier(0.68, -0.55, 0.265, 1.55),
    opacity 0.3s ease;
}

#burger-checkbox {
  display: none;
}

#burger-checkbox:checked + .burger span:nth-child(1) {
  transform: translateY(8px) rotate(45deg);
}

#burger-checkbox:checked + .burger span:nth-child(2) {
  opacity: 0;
  transform: translateX(-20px);
}

#burger-checkbox:checked + .burger span:nth-child(3) {
  transform: translateY(-8px) rotate(-45deg);
}