html, body {
  height: 100%;
  overflow: hidden;
}

#scene {
  position: fixed;
  inset: 0;
  width: 100vw;
  height: 100vh;
  cursor: grab;
  touch-action: none;
  background:
    radial-gradient(ellipse 55% 40% at 25% 15%, rgba(156, 140, 242, 0.12), transparent 60%),
    radial-gradient(ellipse 50% 40% at 80% 75%, rgba(93, 202, 165, 0.08), transparent 60%),
    var(--void);
}
#scene.dragging { cursor: grabbing; }
#scene canvas { display: block; }

#masthead {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 16px;
  padding: 18px 22px;
  pointer-events: none;
  z-index: 5;
}
#masthead .left {
  display: flex;
  align-items: center;
  gap: 14px;
  pointer-events: auto;
}
#masthead .left a.brand { border-bottom: 1px solid transparent; }
#masthead .left a.brand:hover { border-bottom-color: var(--ink-dim); }
#masthead nav {
  display: flex;
  gap: 14px;
}
#masthead nav a {
  font-family: "JetBrains Mono", monospace;
  font-size: 12px;
  color: var(--ink-dim);
  text-decoration: none;
  border-bottom: 1px solid transparent;
}
#masthead nav a:hover { color: var(--ink); border-bottom-color: var(--ink-dim); }
#masthead .hint {
  font-family: "JetBrains Mono", monospace;
  font-size: 11px;
  color: var(--ink-dim);
  text-align: right;
  line-height: 1.5;
  pointer-events: none;
}

#legend {
  position: fixed;
  top: 66px;
  left: 22px;
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
  max-width: 70vw;
  pointer-events: none;
  z-index: 4;
}
#legend .item {
  display: flex;
  align-items: center;
  gap: 6px;
  font-family: "JetBrains Mono", monospace;
  font-size: 11px;
  color: var(--ink-dim);
}
#legend .dot { width: 7px; height: 7px; border-radius: 50%; flex: none; }

#resetBtn, #playBtn, #pauseBtn {
  position: fixed;
  bottom: 22px;
  z-index: 6;
  width: 46px;
  height: 46px;
  border-radius: 50%;
  border: 1px solid var(--hairline);
  background: var(--glass);
  backdrop-filter: blur(10px);
  color: var(--ink);
  font-size: 16px;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  transition: border-color 0.15s ease;
}
#resetBtn:hover, #playBtn:hover, #pauseBtn:hover { border-color: var(--ink-dim); }

#resetBtn {
  left: 22px;
  font-size: 18px;
  opacity: 0;
  transform: scale(0.85);
  pointer-events: none;
  transition: opacity 0.2s ease, transform 0.2s ease, border-color 0.15s ease;
}
#resetBtn.visible {
  opacity: 1;
  transform: scale(1);
  pointer-events: auto;
}

#playBtn { right: 78px; }
#pauseBtn { right: 22px; }

#popup {
  position: fixed;
  left: 50%;
  bottom: 22px;
  transform: translate(-50%, 0);
  width: min(480px, calc(100vw - 44px));
  z-index: 7;
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.22s ease, transform 0.22s ease;
}
#popup.visible {
  opacity: 1;
  transform: translate(-50%, -6px);
  pointer-events: auto;
}
#popup .popup-card {
  position: relative;
  background: var(--glass);
  backdrop-filter: blur(16px);
  border: 1px solid var(--hairline);
  border-radius: var(--radius-lg);
  padding: 22px 24px 20px;
}
#popup .popup-close {
  position: absolute;
  top: 14px;
  right: 14px;
  width: 28px;
  height: 28px;
  border-radius: 50%;
  border: 1px solid var(--hairline);
  background: transparent;
  color: var(--ink-dim);
  font-size: 15px;
  line-height: 1;
  cursor: pointer;
}
#popup .popup-close:hover { color: var(--ink); border-color: var(--ink-dim); }
#popup .crumb {
  font-family: "JetBrains Mono", monospace;
  font-size: 12px;
  color: var(--ink-dim);
  margin: 0 0 8px;
  padding-right: 30px;
}
#popup .crumb .sep { margin: 0 6px; color: var(--hairline); }
#popup .ptitle {
  font-size: 20px;
  font-weight: 600;
  margin: 0 0 8px;
  letter-spacing: -0.01em;
  padding-right: 30px;
}
#popup .desc {
  font-size: 14px;
  line-height: 1.55;
  color: #c4c4dc;
  margin: 0;
}
#popup .note {
  font-size: 12.5px;
  color: var(--ink-dim);
  margin: 10px 0 0;
}
#popup .links {
  display: flex;
  gap: 20px;
  margin-top: 16px;
}
#popup a.link {
  color: var(--core);
  text-decoration: none;
  font-family: "JetBrains Mono", monospace;
  font-size: 13px;
  border-bottom: 1px solid transparent;
}
#popup a.link:hover { border-bottom-color: var(--core); }

@media (max-width: 640px) {
  #masthead { padding: 14px 16px; }
  #masthead .hint { display: none; }
  #legend { top: 56px; left: 16px; }
  #resetBtn, #playBtn, #pauseBtn { bottom: 16px; }
  #resetBtn { left: 16px; }
  #playBtn { right: 72px; }
  #pauseBtn { right: 16px; }
  #popup { bottom: 16px; }
}