body {
  visibility: hidden;/*デフォルトで非表示*/
}

.page-trans__white-bg {
  opacity: 1;
  display: block;
  position: fixed;
  inset: 0; /*top right bottom left を一括指定 */
  width: 100vw;
  height: 100vh;
  background: #ffffff;
  z-index: 1000;
  transition: opacity 0.5s;
  pointer-events: none;
}
.page-trans__white-bg--hide {
  opacity: 0;
}