header {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 105px;
  padding: 0 50px;
  display: flex;
  align-items: center;
  align-content: center;
  justify-content: space-between;
  z-index: 999;
}
header ul {
  display: flex;
}
header ul li {
  position: relative;
  padding: 16px 0;
  margin: 0 5px;
  width: 70px;
  text-align: center;
  font-size: 15px;
  color: #fefcfc;
  opacity: 0.3;
  font-family: "Microsoft Yahei";
}
header ul li::after {
  content: "";
  position: absolute;
  bottom: 0;
  left: 50%;
  width: 0;
  height: 2px;
  transform: translateX(-50%);
  transition: all 0.5s;
  display: block;
  background-color: #bb9b55;
}
header ul li:hover,
header ul li.active {
  color: #fdfbfb;
  opacity: 1;
}
header ul li:hover::after,
header ul li.active::after {
  width: 100%;
}