html, body {
  margin: 0;
  padding: 0;
  width: 100%;
  height: 100%;
  overflow: hidden;
  background-color: #fff; /* blanc */
}

#container {
  position: fixed;
  inset: 0;
  width: 100%;
  height: 100%;
  z-index: 0;   /* 3D = arrière-plan */
}

@media (max-width: 768px) {
  html, body {
    overflow-y: auto;
  }
}