/* ============ Watermark (全局背景 · 稀疏错落) ============ */
body::after {
  content: "";
  position: fixed;
  inset: 0;
  pointer-events: none;
  z-index: 9999;
  background-image: var(--watermark, none);
  background-repeat: repeat;
  background-size: 720px 480px;
}