.header {
  position: fixed;
  top: 0;
  left: 0;
  height: 6.8rem;
  width: 100%;
  z-index: 999;
  background-repeat: no-repeat;
  background-size: cover !important;
  background-image: url("../images/zhaost2.png");
}

.header .down_btn_box {
  width: 100%;  
  height: 6.8rem;
}

.header a {
  display: inline-block;
  width: 100%;
  height: 6.8rem;
}