#page-header.full_page .home-background-slide,
#web_bg .home-background-slide {
  position: absolute;
  inset: 0;
  z-index: 0;
  background-position: center center;
  background-size: cover;
  /* 固定背景会妨碍透明度动画的合成，图层随首页头部定位。 */
  opacity: 0;
  pointer-events: none;
  transition: opacity 1.5s ease-in-out;
  will-change: opacity;
}

#page-header.full_page::before {
  z-index: 1;
  pointer-events: none;
}

/* 保留深色模式下覆盖在底图上的遮罩。 */
#web_bg::before {
  z-index: 1;
  pointer-events: none;
}

#page-header.full_page #site-info,
#page-header.full_page #scroll-down {
  z-index: 2;
}

@media (prefers-reduced-motion: reduce) {
  #page-header.full_page .home-background-slide,
  #web_bg .home-background-slide {
    transition: none;
  }
}