video { 
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    object-fit: cover;
    object-position: center;
	/*-webkit-filter: grayscale(20%);灰度蒙版*/
	background: url("/img/demo-1-bg.jpg") no-repeat;
	background-size: cover;
	display: block; 
}
header {
  position: fixed;
  width: 100%;
  text-align: center;
  color: white;
  transition: .4s;
}
header:hover {
  background: rgba(255,255,255,0.8);
  color: #000;
}
div#fashion {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
}