html,body{
  margin:0; height:100%;
  background: radial-gradient(circle at 50% 40%, #0a0e13 0%, #04060a 70%);
  display:flex; align-items:center; justify-content:center;
  font-family: system-ui, -apple-system, "PingFang SC", "Microsoft YaHei", sans-serif;
  overflow:hidden;
  color:#c9d4e0;
}
canvas{ display:block; border-radius:12px; box-shadow:0 0 80px rgba(0,0,0,.95), 0 0 0 1px #1b2330; }
#err{
  position:fixed; left:8px; top:8px; right:8px;
  color:#ff6b6b; background:rgba(0,0,0,0.85);
  padding:8px 12px; font:12px monospace;
  border-radius:6px; display:none; z-index:9;
  white-space:pre-wrap; max-height:40vh; overflow:auto;
}