:root {
  --bg-deep: #0a0e1a;
  --bg-surface: #111728;
  --bg-elevated: #161d33;
  --bg-elevated-2: #1a2342;

  --accent: #4f7df5;
  --accent-2: #22d3a7;
  --accent-glow: rgba(79, 125, 245, 0.35);

  --text-primary: #e8ecf4;
  --text-secondary: #8a93ad;
  --text-dim: #5b6480;

  --border: rgba(140, 160, 220, 0.10);
  --border-strong: rgba(140, 160, 220, 0.18);

  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 16px;

  --shadow-lg: 0 24px 60px rgba(0,0,0,0.5);
  --shadow-glow: 0 0 0 1px rgba(79,125,245,0.35), 0 8px 28px rgba(79,125,245,0.25);
}

* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; }
body {
  background: var(--bg-deep);
  color: var(--text-primary);
  font-family: ui-sans-serif, system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  -webkit-font-smoothing: antialiased;
}

/* ============================================================
   Section
   ============================================================ */
.system-expansion {
  position: relative;
  overflow: hidden;
  padding: clamp(80px, 10vw, 140px) clamp(20px, 5vw, 64px);
  isolation: isolate;
}

.se-bg-grid {
  position: absolute;
  inset: 0;
  background-image:
    linear-gradient(rgba(140,160,220,0.05) 1px, transparent 1px),
    linear-gradient(90deg, rgba(140,160,220,0.05) 1px, transparent 1px);
  background-size: 56px 56px;
  -webkit-mask-image: radial-gradient(ellipse at center, #000 25%, transparent 78%);
          mask-image: radial-gradient(ellipse at center, #000 25%, transparent 78%);
  z-index: -2;
}

.se-bg-glow {
  position: absolute;
  border-radius: 50%;
  filter: blur(90px);
  z-index: -1;
  pointer-events: none;
}
.se-bg-glow-1 {
  top: 10%; left: -10%;
  width: 50vw; height: 50vw;
  max-width: 700px; max-height: 700px;
  background: radial-gradient(circle, var(--accent-glow) 0%, transparent 60%);
  animation: se-drift-1 20s ease-in-out infinite alternate;
}
.se-bg-glow-2 {
  bottom: -10%; right: -10%;
  width: 55vw; height: 55vw;
  max-width: 760px; max-height: 760px;
  background: radial-gradient(circle, rgba(34,211,167,0.22) 0%, transparent 60%);
  animation: se-drift-2 25s ease-in-out infinite alternate;
}
@keyframes se-drift-1 { to { transform: translate(40px, 30px) scale(1.1); } }
@keyframes se-drift-2 { to { transform: translate(-40px, -20px) scale(1.08); } }

/* ============================================================
   Container
   ============================================================ */
.expand-container {
  max-width: 1280px;
  margin: 0 auto;
}

/* ============================================================
   Header
   ============================================================ */
.expand-header {
  text-align: center;
  max-width: 720px;
  margin: 0 auto clamp(48px, 7vw, 80px);
  animation: se-fade-up .8s ease both;
}

.se-eyebrow {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 6px 14px;
  border: 1px solid var(--border-strong);
  border-radius: 999px;
  font-size: 12px;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--text-secondary);
  background: rgba(255,255,255,0.02);
  backdrop-filter: blur(8px);
  margin-bottom: 24px;
}
.se-eyebrow-dot {
  width: 6px; height: 6px;
  border-radius: 50%;
  background: var(--accent-2);
  box-shadow: 0 0 12px var(--accent-2);
  animation: se-blink 2s ease-in-out infinite;
}
@keyframes se-blink {
  0%, 100% { opacity: 1; }
  50%      { opacity: 0.3; }
}

.expand-header h2 {
  font-size: clamp(34px, 4.6vw, 58px);
  line-height: 1.05;
  font-weight: 700;
  letter-spacing: -0.02em;
  margin: 0 0 18px;
}
.se-gradient-text {
  background: linear-gradient(120deg, var(--accent) 0%, var(--accent-2) 100%);
  -webkit-background-clip: text;
          background-clip: text;
  color: transparent;
}
.expand-header p {
  font-size: clamp(15px, 1.2vw, 17px);
  line-height: 1.7;
  color: var(--text-secondary);
  margin: 0;
}

/* ============================================================
   Visual: horizontal growth axis
   ============================================================ */
.expand-visual {
  position: relative;
  width: 100%;
  height: clamp(360px, 38vw, 460px);
  margin: 0 auto clamp(56px, 7vw, 88px);
  border-radius: 24px;
  background:
    radial-gradient(ellipse at 15% 50%, rgba(79,125,245,0.10) 0%, transparent 55%),
    radial-gradient(ellipse at 90% 50%, rgba(34,211,167,0.08) 0%, transparent 55%),
    linear-gradient(180deg, var(--bg-elevated) 0%, var(--bg-surface) 100%);
  border: 1px solid var(--border);
  box-shadow: var(--shadow-lg), inset 0 1px 0 rgba(255,255,255,0.04);
  overflow: hidden;
  animation: se-zoom-in .8s cubic-bezier(.2,.7,.2,1) both;
}
@keyframes se-zoom-in {
  from { opacity: 0; transform: scale(0.97); }
  to   { opacity: 1; transform: scale(1); }
}

.expand-svg {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  pointer-events: none;
}

.expand-spine { opacity: 0.6; }
.expand-branch { opacity: 0.7; }
.expand-pulse { filter: drop-shadow(0 0 6px var(--accent-2)); }

/* CORE pillar (left side) */
.expand-core {
  position: absolute;
  top: 50%;
  left: clamp(24px, 5%, 60px);
  transform: translateY(-50%);
  width: 160px;
  height: 220px;
  border-radius: 20px;
  background: linear-gradient(180deg, var(--bg-elevated-2) 0%, var(--bg-surface) 100%);
  border: 1px solid var(--accent);
  box-shadow:
    inset 0 0 0 1px rgba(255,255,255,0.05),
    0 0 60px var(--accent-glow),
    var(--shadow-lg);
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  padding: 18px;
  z-index: 2;
  overflow: hidden;
}

.expand-core-glow {
  position: absolute;
  inset: -1px;
  border-radius: 20px;
  background: linear-gradient(180deg, var(--accent), var(--accent-2));
  opacity: 0.18;
  filter: blur(20px);
  z-index: -1;
}

.expand-core-bars {
  display: flex;
  align-items: flex-end;
  gap: 6px;
  height: 80px;
}
.expand-core-bars span {
  flex: 1;
  background: linear-gradient(180deg, var(--accent-2), var(--accent));
  border-radius: 3px;
  opacity: 0.6;
  animation: se-bar 2.2s ease-in-out infinite;
}
.expand-core-bars span:nth-child(1) { height: 40%; animation-delay: 0s;   }
.expand-core-bars span:nth-child(2) { height: 75%; animation-delay: .2s;  }
.expand-core-bars span:nth-child(3) { height: 55%; animation-delay: .4s;  }
.expand-core-bars span:nth-child(4) { height: 90%; animation-delay: .6s;  }

@keyframes se-bar {
  0%, 100% { transform: scaleY(0.85); opacity: 0.55; }
  50%      { transform: scaleY(1.05); opacity: 1; }
}

.expand-core-label { text-align: left; }
.expand-core-tag {
  display: block;
  font-size: 10px;
  letter-spacing: 0.22em;
  text-transform: uppercase;
  color: var(--accent-2);
  margin-bottom: 6px;
}
.expand-core-name {
  display: block;
  font-size: 18px;
  font-weight: 700;
  color: var(--text-primary);
  letter-spacing: -0.01em;
}

/* EXTENSION nodes */
.expand-node {
  position: absolute;
  width: 180px;
  padding: 16px;
  background: linear-gradient(180deg, var(--bg-elevated-2) 0%, var(--bg-surface) 100%);
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-lg);
  z-index: 3;
  transition: transform .3s cubic-bezier(.2,.7,.2,1), border-color .3s ease, box-shadow .3s ease;
  animation: se-fade-up .8s ease both;
}
.expand-node:hover {
  transform: translateY(-4px);
  border-color: var(--accent);
  box-shadow: var(--shadow-glow), var(--shadow-lg);
}

.expand-n1 { top: 10%;  left: 48%; animation-delay: .1s; }
.expand-n2 { top: 38%;  left: 65%; animation-delay: .25s; }
.expand-n3 { bottom: 10%; left: 48%; animation-delay: .4s; }

.expand-node-tag {
  display: inline-block;
  padding: 2px 8px;
  font-size: 10px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--bg-deep);
  background: var(--accent-2);
  border-radius: 999px;
  margin-bottom: 12px;
  font-weight: 700;
}
.expand-node-tag-soon {
  background: transparent;
  color: var(--text-secondary);
  border: 1px solid var(--border-strong);
}

.expand-node-icon {
  width: 36px;
  height: 36px;
  border-radius: 10px;
  background: linear-gradient(135deg, rgba(79,125,245,0.2), rgba(34,211,167,0.15));
  border: 1px solid var(--border-strong);
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--accent-2);
  margin-bottom: 12px;
}

.expand-node-title {
  font-size: 15px;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 4px;
}

.expand-node-sub {
  font-size: 12px;
  color: var(--text-dim);
  letter-spacing: 0.02em;
}

/* horizon caret */
.expand-horizon {
  position: absolute;
  top: 50%;
  right: 18px;
  transform: translateY(-50%);
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 10px;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--text-dim);
  z-index: 2;
  animation: se-horizon 2s ease-in-out infinite;
}
@keyframes se-horizon {
  0%, 100% { transform: translate(0, -50%); opacity: .5; }
  50%      { transform: translate(6px, -50%); opacity: 1; }
}

/* ============================================================
   Explanation grid (3 cards with flow line)
   ============================================================ */
.expand-text {
  position: relative;
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 24px;
}

.expand-flow-line {
  position: absolute;
  top: 36px;
  left: 8%;
  right: 8%;
  height: 1px;
  background: linear-gradient(90deg,
    transparent,
    var(--accent) 15%,
    var(--accent-2) 85%,
    transparent);
  opacity: 0.4;
  z-index: 0;
}

.expand-point {
  position: relative;
  padding: 28px 24px 24px;
  background: linear-gradient(180deg, var(--bg-elevated-2) 0%, var(--bg-surface) 100%);
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-lg);
  transition: transform .3s ease, border-color .3s ease, box-shadow .3s ease;
  animation: se-fade-up .8s ease both;
  z-index: 1;
}
.expand-point:nth-child(2) { animation-delay: .1s; }
.expand-point:nth-child(3) { animation-delay: .15s; }
.expand-point:nth-child(4) { animation-delay: .2s; }

.expand-point:hover {
  transform: translateY(-4px);
  border-color: var(--accent);
  box-shadow: var(--shadow-glow);
}

.expand-point-num {
  position: absolute;
  top: -16px;
  left: 24px;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  background: var(--bg-deep);
  border: 1px solid var(--accent);
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  font-size: 12px;
  font-weight: 700;
  color: var(--accent-2);
  box-shadow: 0 0 0 4px var(--bg-deep), 0 0 20px var(--accent-glow);
}

.expand-point span {
  display: block;
  font-size: 16px;
  font-weight: 700;
  color: var(--text-primary);
  margin: 12px 0 10px;
  letter-spacing: -0.01em;
}

.expand-point p {
  margin: 0;
  font-size: 13.5px;
  line-height: 1.65;
  color: var(--text-secondary);
}

/* ============================================================
   Responsive
   ============================================================ */
@media (max-width: 960px) {
  .expand-visual { height: 520px; }
  .expand-core {
    top: 24px; left: 50%;
    transform: translateX(-50%);
    width: 80%;
    height: 120px;
    flex-direction: row;
    align-items: center;
    gap: 16px;
  }
  .expand-core-bars { width: 80px; height: 60px; }
  .expand-core-label { flex: 1; }

  .expand-svg { display: none; }
  .expand-horizon { display: none; }

  .expand-n1, .expand-n2, .expand-n3 {
    position: relative;
    top: auto; left: auto; bottom: auto;
    width: auto;
    margin: 0 auto;
  }

  .expand-visual {
    display: flex;
    flex-direction: column;
    justify-content: flex-start;
    align-items: stretch;
    padding: 20px;
    gap: 16px;
    height: auto;
  }
  .expand-core { position: relative; transform: none; left: auto; top: auto; width: 100%; }
}

@media (max-width: 720px) {
  .expand-text { grid-template-columns: 1fr; gap: 32px; }
  .expand-flow-line { display: none; }
  .expand-core { flex-direction: column; height: auto; padding: 20px; }
  .expand-core-bars { width: 100%; }
}

/* ============================================================
   Animations
   ============================================================ */
@keyframes se-fade-up {
  from { opacity: 0; transform: translateY(20px); }
  to   { opacity: 1; transform: translateY(0); }
}

@media (prefers-reduced-motion: reduce) {
  .se-bg-glow-1, .se-bg-glow-2,
  .expand-core-bars span,
  .expand-horizon,
  .expand-pulse,
  .se-eyebrow-dot { animation: none !important; }
}