:root {
  --bg-base:        #080c14;
  --bg-surface:     #0d1321;
  --bg-card:        #101828;
  --bg-elevated:    #1a2540;
  --border:         #1e2d3d;
  --border-bright:  #2a3f57;
  --text-primary:   #e2e8f0;
  --text-secondary: #8892a4;
  --text-muted:     #4a5568;
  --cyan:    #00d4ff;
  --green:   #00ff9f;
  --red:     #ff4757;
  --orange:  #ffa502;
  --purple:  #a78bfa;
  --cyan-dim:   rgba(0, 212, 255, 0.12);
  --green-dim:  rgba(0, 255, 159, 0.10);
  --orange-dim: rgba(255, 165, 2, 0.12);
  --font-mono: 'JetBrains Mono', 'Courier New', monospace;
  --font-sans: 'Inter', system-ui, sans-serif;
  --radius:    8px;
  --radius-lg: 12px;
  --transition: 200ms ease;
}

*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }

body {
  background: var(--bg-base);
  color: var(--text-primary);
  font-family: var(--font-sans);
  font-size: 14px;
  line-height: 1.6;
  min-height: 100vh;
  overflow-x: hidden;
}

.mono { font-family: var(--font-mono); }

/* ===== BACKGROUND ===== */
.bg-grid {
  position: fixed; inset: 0;
  background-image:
    linear-gradient(rgba(0, 212, 255, 0.025) 1px, transparent 1px),
    linear-gradient(90deg, rgba(0, 212, 255, 0.025) 1px, transparent 1px);
  background-size: 50px 50px;
  pointer-events: none; z-index: 0;
}
.bg-glow {
  position: fixed; top: -30vh; left: 50%; transform: translateX(-50%);
  width: 80vw; height: 60vh;
  background: radial-gradient(ellipse at center, rgba(0, 212, 255, 0.04) 0%, transparent 70%);
  pointer-events: none; z-index: 0;
}
.scanline {
  position: fixed; inset: 0;
  background: repeating-linear-gradient(to bottom,
    transparent 0, transparent 3px,
    rgba(0, 0, 0, 0.06) 3px, rgba(0, 0, 0, 0.06) 4px);
  pointer-events: none; z-index: 1; opacity: 0.4;
}

/* ===== HEADER ===== */
header {
  position: sticky; top: 0; z-index: 100;
  display: flex; justify-content: space-between; align-items: center;
  padding: 1rem 2rem;
  background: rgba(8, 12, 20, 0.92);
  border-bottom: 1px solid var(--border);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
}

.header-left { display: flex; flex-direction: column; gap: 2px; }
.logo { font-size: 1.4rem; font-weight: 700; letter-spacing: 3px; line-height: 1; }
.logo-bracket { color: var(--text-muted); }
.logo-accent  { color: var(--cyan); text-shadow: 0 0 20px rgba(0, 212, 255, 0.4); }
.tagline { font-size: 11px; color: var(--text-muted); letter-spacing: 1px; }

.back-btn {
  font-size: 11px; letter-spacing: 1px;
  color: var(--text-secondary); text-decoration: none;
  border: 1px solid var(--border); border-radius: 4px;
  padding: 5px 12px; transition: all var(--transition);
}
.back-btn:hover { border-color: var(--cyan); color: var(--cyan); background: var(--cyan-dim); }

/* ===== CONTROLS ===== */
.controls {
  position: relative; z-index: 10;
  display: flex; align-items: center; gap: 1rem; flex-wrap: wrap;
  padding: 0.75rem 2rem;
  background: var(--bg-surface);
  border-bottom: 1px solid var(--border);
}

.ctrl-group { display: flex; align-items: center; gap: 8px; }

.ctrl-btn {
  background: transparent;
  border: 1px solid var(--border);
  border-radius: 4px;
  color: var(--text-secondary);
  font-family: var(--font-mono); font-size: 11px; font-weight: 600;
  letter-spacing: 1px; padding: 6px 14px;
  cursor: pointer; transition: all var(--transition);
}
.ctrl-btn:hover:not(:disabled) {
  border-color: var(--cyan); color: var(--cyan); background: var(--cyan-dim);
}
.ctrl-btn:disabled { opacity: 0.35; cursor: not-allowed; }
.ctrl-btn.primary {
  border-color: var(--green); color: var(--green); background: var(--green-dim);
}
.ctrl-btn.primary:hover:not(:disabled) {
  box-shadow: 0 0 12px rgba(0, 255, 159, 0.2);
}
.ctrl-btn.active { border-color: var(--orange); color: var(--orange); background: var(--orange-dim); }

/* Wireshark toggle */
.ws-toggle-label {
  display: flex; align-items: center; gap: 8px;
  font-size: 11px; letter-spacing: 1px;
  color: var(--text-muted); cursor: pointer; user-select: none;
}
.ws-toggle-input { display: none; }
.ws-toggle-track {
  width: 32px; height: 16px;
  background: var(--border); border-radius: 8px;
  position: relative; flex-shrink: 0;
  transition: background var(--transition);
}
.ws-toggle-track::after {
  content: ''; position: absolute;
  top: 2px; left: 2px; width: 12px; height: 12px;
  background: var(--text-muted); border-radius: 50%;
  transition: left var(--transition), background var(--transition);
}
.ws-toggle-input:checked + .ws-toggle-track { background: rgba(0, 212, 255, 0.3); }
.ws-toggle-input:checked + .ws-toggle-track::after { left: 18px; background: var(--cyan); }

.step-counter { font-size: 11px; letter-spacing: 1px; color: var(--text-muted); margin-left: auto; }

/* ===== TOPOLOGY ===== */
.topology-section {
  position: relative; z-index: 5;
  padding: 1.5rem 2rem 1rem;
  background: var(--bg-surface);
  border-bottom: 1px solid var(--border);
}

.topology-scroll { overflow-x: auto; }

.topology-track {
  position: relative;
  display: flex; align-items: flex-start;
  max-width: 1100px; margin: 0 auto;
  min-width: 620px;
}

/* Nodes */
.topo-node {
  display: flex; flex-direction: column; align-items: center;
  gap: 5px; flex-shrink: 0; min-width: 72px;
}

.node-body {
  width: 56px; height: 56px;
  border: 2px solid var(--border);
  border-radius: var(--radius);
  background: var(--bg-card);
  display: flex; align-items: center; justify-content: center;
  font-size: 1.5rem;
  transition: border-color var(--transition), background var(--transition), box-shadow var(--transition);
  will-change: border-color, box-shadow;
}
.node-label { font-size: 9px; letter-spacing: 1.5px; color: var(--text-muted); text-align: center; }
.node-sub   { font-size: 8px; color: var(--text-muted); opacity: 0.65; text-align: center; }

/* Node states */
.topo-node.active .node-body {
  border-color: var(--cyan);
  background: rgba(0, 212, 255, 0.08);
  box-shadow: 0 0 16px rgba(0, 212, 255, 0.3), 0 0 4px rgba(0, 212, 255, 0.5) inset;
}
.topo-node.active .node-label { color: var(--cyan); }
.topo-node.visited .node-body {
  border-color: var(--green);
  background: rgba(0, 255, 159, 0.06);
}
.topo-node.visited .node-label { color: var(--green); opacity: 0.8; }

/* Connectors */
.topo-connector {
  flex: 1;
  height: 2px;
  background: var(--border);
  align-self: flex-start;
  /* Align center of 2px connector with center of 56px node-body: (56/2) - (2/2) = 27px */
  margin-top: 27px;
  transition: background 0.5s ease, box-shadow 0.5s ease;
  min-width: 16px;
}
.topo-connector.active {
  background: var(--cyan);
  box-shadow: 0 0 6px rgba(0, 212, 255, 0.5);
}
.topo-connector.done {
  background: var(--green);
  box-shadow: 0 0 4px rgba(0, 255, 159, 0.3);
}

/* Packet dot */
.packet-dot {
  position: absolute;
  width: 14px; height: 14px;
  border-radius: 50%;
  background: var(--cyan);
  box-shadow: 0 0 10px var(--cyan), 0 0 20px rgba(0, 212, 255, 0.5);
  /* Center vertically on the connector: connector center = 28px, dot half = 7px → top = 21px */
  top: 21px;
  transform: translateX(-50%);
  z-index: 10;
  pointer-events: none;
  transition: left 0.7s cubic-bezier(0.4, 0, 0.2, 1);
}

/* ===== STEP BANNER ===== */
.step-banner {
  position: relative; z-index: 5;
  display: flex; align-items: flex-start; gap: 12px;
  padding: 1rem 2rem;
  background: var(--bg-card);
  border-bottom: 1px solid var(--border);
}
.step-badge {
  font-size: 10px; letter-spacing: 1.5px;
  border: 1px solid var(--border);
  border-radius: 4px; padding: 3px 10px;
  color: var(--text-muted); white-space: nowrap;
  flex-shrink: 0; margin-top: 3px;
}
.step-badge.active { border-color: var(--cyan);  color: var(--cyan); }
.step-badge.done   { border-color: var(--green); color: var(--green); }
.step-title { font-size: 1rem; font-weight: 600; color: var(--text-primary); }
.step-desc  { font-size: 13px; color: var(--text-secondary); margin-top: 4px; line-height: 1.6; }

/* ===== PANELS ROW ===== */
.panels-row {
  position: relative; z-index: 5;
  display: grid; grid-template-columns: 1fr 1fr;
  gap: 1rem; padding: 1rem 2rem;
}

.panel {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  overflow: hidden;
}

.panel-hdr {
  padding: 10px 14px;
  background: var(--bg-elevated);
  border-bottom: 1px solid var(--border);
}
.panel-title {
  font-size: 10px; letter-spacing: 1.5px;
  color: var(--text-muted); font-weight: 600;
}

/* Layer blocks */
.layer-block {
  padding: 10px 14px;
  border-bottom: 1px solid var(--border);
}
.layer-block:last-child { border-bottom: none; }

.layer-label {
  font-size: 10px; font-weight: 700; letter-spacing: 1.5px;
  display: flex; align-items: center; gap: 8px;
  margin-bottom: 8px;
}
.layer-badge {
  font-size: 8px; padding: 1px 5px;
  border-radius: 3px; border: 1px solid currentColor; opacity: 0.6;
}
.eth-accent { color: var(--cyan); }
.ip-accent  { color: var(--green); }
.tcp-accent { color: var(--purple); }

/* Field grid */
.field-grid {
  display: grid; grid-template-columns: auto 1fr;
  gap: 4px 16px; align-items: center;
}
.field-key {
  font-size: 10px; color: var(--text-muted); letter-spacing: 0.5px; white-space: nowrap;
}
.field-val {
  font-size: 11px; color: var(--text-secondary);
  transition: color var(--transition), text-shadow var(--transition);
}
.field-val.changed {
  color: var(--orange);
  text-shadow: 0 0 8px rgba(255, 165, 2, 0.4);
  animation: flash-change 0.7s ease;
}
.field-val.settled { color: var(--green); }

@keyframes flash-change {
  0%, 100% { background: transparent; }
  30% { background: rgba(255, 165, 2, 0.12); border-radius: 3px; }
}

/* ===== CHANGES PANEL ===== */
.changes-list {
  padding: 12px 14px;
  display: flex; flex-direction: column; gap: 8px;
}
.changes-empty {
  font-size: 11px; color: var(--text-muted); letter-spacing: 0.5px;
}

.change-item {
  padding: 8px 10px;
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-left: 3px solid var(--orange);
  border-radius: 4px;
  display: flex; flex-direction: column; gap: 3px;
  animation: slide-in 0.3s ease;
}
.change-item.info { border-left-color: var(--cyan); }

.change-field {
  font-family: var(--font-mono); font-size: 10px;
  font-weight: 700; letter-spacing: 0.5px; color: var(--orange);
}
.change-item.info .change-field { color: var(--cyan); }

.change-from-to {
  font-family: var(--font-mono); font-size: 11px; color: var(--text-secondary);
}
.change-from-to .from  { color: var(--red); text-decoration: line-through; opacity: 0.8; }
.change-from-to .arrow { color: var(--text-muted); margin: 0 4px; }
.change-from-to .to    { color: var(--green); }

.change-reason { font-size: 11px; color: var(--text-muted); font-style: italic; }

@keyframes slide-in {
  from { opacity: 0; transform: translateX(-8px); }
  to   { opacity: 1; transform: translateX(0); }
}

/* ===== WIRESHARK SECTION ===== */
.wireshark-section {
  position: relative; z-index: 5;
  margin: 0 2rem 1rem;
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  overflow: hidden;
}

.ws-panel-hdr {
  display: flex; align-items: center; gap: 8px;
  padding: 10px 16px;
  background: rgba(0, 212, 255, 0.06);
  border-bottom: 1px solid var(--border);
}
.ws-panel-title {
  font-size: 11px; letter-spacing: 1px; color: var(--cyan);
}

.ws-body {
  padding: 12px 16px;
  background: var(--bg-card);
  overflow-x: auto;
}
.ws-placeholder {
  font-size: 11px; color: var(--text-muted); letter-spacing: 0.5px;
}

/* Wireshark tree */
.ws-tree { display: flex; flex-direction: column; gap: 2px; }

.ws-section-hdr {
  display: flex; align-items: center; gap: 6px;
  font-family: var(--font-mono); font-size: 11px;
  color: var(--text-secondary); letter-spacing: 0.3px;
  padding: 3px 0; cursor: pointer; user-select: none;
}
.ws-section-hdr:hover { color: var(--text-primary); }

.ws-chevron {
  font-size: 9px; color: var(--text-muted);
  transition: transform 0.18s ease; flex-shrink: 0;
}
.ws-section.open .ws-chevron { transform: rotate(90deg); }

.ws-fields { display: none; padding-left: 18px; padding-bottom: 4px; }
.ws-section.open .ws-fields { display: flex; flex-direction: column; gap: 1px; }

.ws-field {
  display: flex; gap: 12px;
  font-family: var(--font-mono); font-size: 10.5px;
  color: var(--text-secondary); padding: 1px 0;
}
.ws-field-name {
  color: var(--text-muted);
  min-width: 200px; flex-shrink: 0;
}
.ws-field-val { color: var(--cyan); }
.ws-field-val.changed { color: var(--orange); }

/* ===== FOOTER ===== */
footer {
  position: relative; z-index: 10;
  padding: 1rem 2rem;
  border-top: 1px solid var(--border);
  background: var(--bg-surface);
  text-align: center;
}
.footer-text { font-size: 11px; color: var(--text-muted); letter-spacing: 0.5px; }

/* ===== MISC ===== */
.cursor.blink { animation: blink 1s step-end infinite; }
@keyframes blink { 0%, 100% { opacity: 1; } 50% { opacity: 0; } }

::-webkit-scrollbar { width: 6px; height: 6px; }
::-webkit-scrollbar-track { background: var(--bg-base); }
::-webkit-scrollbar-thumb { background: var(--border-bright); border-radius: 3px; }
::-webkit-scrollbar-thumb:hover { background: var(--cyan); }

::selection { background: rgba(0, 212, 255, 0.25); color: var(--text-primary); }

/* ===== RESPONSIVE ===== */
@media (max-width: 900px) {
  .panels-row { grid-template-columns: 1fr; }
  header { padding: 0.75rem 1rem; }
  .controls { padding: 0.75rem 1rem; }
  .topology-section { padding: 1rem 1rem 0.75rem; }
  .panels-row { padding: 0.75rem 1rem; }
  .wireshark-section { margin: 0 1rem 1rem; }
  .step-banner { padding: 0.75rem 1rem; }
}

@media (max-width: 600px) {
  .controls { flex-direction: column; align-items: flex-start; }
  .step-counter { margin-left: 0; }
  .ws-field-name { min-width: 140px; }
}