html, body {
  height: 100%;
  margin: 0;
  padding: 0;
}

body::before {
  content: "";
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: url('pic/bg-main.webp') no-repeat center center;
  background-size: cover;
  opacity: 0.2;
  z-index: -1;
}