:root {
  --bg: #0f172a;
  --bg-2: #111c36;
  --panel: #1a2547;
  --ink: #e8eefc;
  --ink-dim: #9aa8c7;
  --accent: #5eead4;
  --accent-2: #818cf8;
  --warn: #fbbf24;
  --good: #34d399;
  --bad: #f87171;
  --line: rgba(255,255,255,0.08);
  --radius: 14px;
  --maxw: 1000px;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  background: var(--bg);
  color: var(--ink);
  line-height: 1.55;
  -webkit-font-smoothing: antialiased;
}

h1, h2, h3, h4 { line-height: 1.15; margin: 0 0 0.6em; }
h2 { font-size: clamp(1.8rem, 3vw, 2.6rem); }
p { margin: 0 0 1em; }
em { font-style: italic; color: var(--accent); }

/* Aim indicator (shows the lesson aim the current section targets) */
#aim-indicator {
  position: fixed;
  top: 18px;
  left: 50%;
  transform: translate(-50%, -12px);
  background: rgba(20, 30, 60, 0.45);
  border: 1px solid rgba(94, 234, 212, 0.35);
  color: rgba(232, 238, 252, 0.75);
  padding: 7px 18px;
  border-radius: 999px;
  font-size: 0.82rem;
  z-index: 60;
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.35s ease, transform 0.35s ease;
  backdrop-filter: blur(6px);
  -webkit-backdrop-filter: blur(6px);
  text-align: center;
  line-height: 1.2;
  white-space: nowrap;
  max-width: calc(100vw - 40px);
  overflow: hidden;
  text-overflow: ellipsis;
}
#aim-indicator.visible {
  opacity: 0.85;
  transform: translate(-50%, 0);
}
#aim-indicator::before {
  content: "🎯 Aim: ";
  color: rgba(94, 234, 212, 0.85);
  font-weight: 600;
}
@media (max-width: 700px) {
  #aim-indicator { font-size: 0.72rem; padding: 5px 12px; }
}

/* Progress bar */
#progress-bar {
  position: fixed; top: 0; left: 0;
  height: 4px; width: 0%;
  background: linear-gradient(90deg, var(--accent), var(--accent-2));
  z-index: 100;
  transition: width 0.1s linear;
}

/* Side nav */
#side-nav {
  position: fixed;
  left: 22px; top: 50%;
  transform: translateY(-50%);
  display: flex; flex-direction: column; gap: 14px;
  z-index: 50;
}
#side-nav a {
  position: relative;
  width: 12px; height: 12px;
  border-radius: 50%;
  background: rgba(255,255,255,0.18);
  transition: background 0.2s, transform 0.2s;
}
#side-nav a:hover { background: var(--accent); transform: scale(1.2); }
#side-nav a.active { background: var(--accent); transform: scale(1.3); }
#side-nav a::after {
  content: attr(data-label);
  position: absolute;
  left: 22px; top: 50%;
  transform: translateY(-50%);
  background: var(--panel);
  color: var(--ink);
  font-size: 0.78rem;
  padding: 4px 10px;
  border-radius: 6px;
  white-space: nowrap;
  opacity: 0; pointer-events: none;
  transition: opacity 0.18s;
}
#side-nav a:hover::after { opacity: 1; }

/* Sections */
.section {
  min-height: 100vh;
  display: flex;
  align-items: center;
  padding: 80px 24px;
  border-bottom: 1px solid var(--line);
}
.container {
  width: 100%;
  max-width: var(--maxw);
  margin: 0 auto;
}
.sub { color: var(--ink-dim); font-size: 1.1rem; max-width: 70ch; }
.muted { color: var(--ink-dim); }
.feedback { min-height: 1.5em; font-weight: 500; }
.feedback.good { color: var(--good); }
.feedback.bad { color: var(--bad); }

/* Hero */
.hero {
  background:
    radial-gradient(1200px 600px at 80% 10%, rgba(94,234,212,0.15), transparent 60%),
    radial-gradient(900px 500px at 10% 80%, rgba(129,140,248,0.18), transparent 60%),
    var(--bg);
}
.hero-inner { max-width: 900px; margin: 0 auto; text-align: center; }
.hero h1 {
  font-size: clamp(2.8rem, 7vw, 5.5rem);
  letter-spacing: -0.02em;
}
.accent { color: var(--accent); }
.eyebrow {
  text-transform: uppercase;
  letter-spacing: 0.2em;
  color: var(--accent-2);
  font-size: 0.85rem;
  margin-bottom: 1em;
}
.lead { font-size: 1.2rem; color: var(--ink-dim); max-width: 60ch; margin: 0 auto 2em; }
.scroll-cue {
  display: inline-block;
  padding: 12px 22px;
  border: 1px solid var(--accent);
  color: var(--accent);
  border-radius: 999px;
  text-decoration: none;
  font-weight: 500;
  transition: background 0.2s, color 0.2s;
}
.scroll-cue:hover { background: var(--accent); color: var(--bg); }

/* Objectives */
.objectives-list {
  list-style: none; padding: 0;
  display: grid; gap: 12px;
  margin-top: 1.5em;
}
.objectives-list li {
  background: var(--panel);
  padding: 16px 20px;
  border-radius: var(--radius);
  border-left: 4px solid var(--accent);
  font-size: 1.05rem;
}

/* Flip cards */
.flip-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 20px;
  margin: 1.5em 0;
}
.flip-card {
  perspective: 1200px;
  background: transparent;
  border: none;
  padding: 0;
  cursor: pointer;
  font: inherit;
  color: inherit;
  text-align: left;
  min-height: 200px;
}
.flip-card.small { min-height: 200px; }
.flip-card.small .flip-face { padding: 16px; }
.flip-card.small .flip-front h3 { font-size: 1.1rem; }
.flip-card.small .flip-back p {
  font-size: 0.88rem;
  line-height: 1.4;
  margin: 0;
}
.flip-inner {
  position: relative;
  width: 100%;
  height: 100%;
  min-height: inherit;
  transition: transform 0.6s;
  transform-style: preserve-3d;
}
.flip-card[aria-pressed="true"] .flip-inner {
  transform: rotateY(180deg);
}
.flip-face {
  position: absolute;
  inset: 0;
  padding: 22px;
  border-radius: var(--radius);
  backface-visibility: hidden;
  display: flex;
  flex-direction: column;
  justify-content: center;
  background: var(--panel);
  border: 1px solid var(--line);
}
.flip-front h3 { margin-bottom: 0.3em; }
.flip-front .hint {
  color: var(--ink-dim);
  font-size: 0.85rem;
  margin: 0;
  text-transform: uppercase;
  letter-spacing: 0.1em;
}
.flip-back {
  background: linear-gradient(135deg, #1f2a55 0%, #1a2547 100%);
  transform: rotateY(180deg);
  border-color: var(--accent);
}
.flip-back p { margin: 0; }

/* Callout chips */
.callout {
  margin-top: 1.5em;
  padding: 16px 20px;
  background: rgba(94,234,212,0.06);
  border: 1px dashed rgba(94,234,212,0.4);
  border-radius: var(--radius);
}
.callout.note {
  background: rgba(251,191,36,0.06);
  border-color: rgba(251,191,36,0.4);
  margin-top: 1.5em;
}
.chip {
  display: inline-block;
  background: var(--panel);
  padding: 4px 12px;
  margin: 0 4px;
  border-radius: 999px;
  font-size: 0.9rem;
}

.worksheet-callout {
  margin-top: 2em;
  padding: 16px 20px;
  background: rgba(129,140,248,0.1);
  border: 1px solid rgba(129,140,248,0.4);
  border-radius: var(--radius);
  font-size: 1.05rem;
}

/* URL */
.url-line {
  font-family: "SF Mono", Menlo, Consolas, monospace;
  font-size: clamp(1.1rem, 2.4vw, 1.8rem);
  background: var(--panel);
  padding: 22px;
  border-radius: var(--radius);
  margin: 1.5em 0 1em;
  border: 1px solid var(--line);
  word-break: break-all;
}
.url-part {
  cursor: pointer;
  padding: 4px 2px;
  border-radius: 4px;
  transition: background 0.15s, color 0.15s;
}
.url-part:hover { background: rgba(255,255,255,0.08); }
.url-part.active {
  background: var(--accent);
  color: var(--bg);
  font-weight: 600;
}
.url-part[data-key="protocol"]  { color: #5eead4; }
.url-part[data-key="subdomain"] { color: #fbbf24; }
.url-part[data-key="domain"]    { color: #f472b6; }
.url-part[data-key="directory"] { color: #818cf8; }
.url-part[data-key="filename"]  { color: #34d399; }
.url-part.active { color: var(--bg) !important; }

.url-explainer {
  background: var(--panel);
  padding: 22px;
  border-radius: var(--radius);
  min-height: 120px;
  border: 1px solid var(--line);
}
.url-explainer h3 { margin-bottom: 0.3em; color: var(--accent); }

/* TLD game */
.tld-game {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 30px;
  margin: 1.5em 0;
}
.tld-col {
  display: flex;
  flex-direction: column;
  gap: 10px;
}
.tld-btn {
  background: var(--panel);
  color: var(--ink);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 14px 18px;
  font-size: 1.05rem;
  cursor: pointer;
  text-align: left;
  transition: all 0.15s;
  font-family: inherit;
}
.tld-btn:hover:not(.matched):not(.selected) { border-color: var(--accent); }
.tld-btn.selected { border-color: var(--accent); background: rgba(94,234,212,0.1); }
.tld-btn.matched {
  background: rgba(52,211,153,0.1);
  border-color: var(--good);
  color: var(--good);
  cursor: default;
}
.tld-btn.wrong {
  animation: shake 0.3s;
  border-color: var(--bad);
}
@keyframes shake {
  0%, 100% { transform: translateX(0); }
  25% { transform: translateX(-8px); }
  75% { transform: translateX(8px); }
}
.tld-controls {
  display: flex; gap: 12px; align-items: center; flex-wrap: wrap;
  margin-top: 1em;
}
.score { color: var(--ink-dim); margin-right: auto; }

.btn {
  background: var(--accent);
  color: var(--bg);
  border: none;
  padding: 10px 18px;
  font: inherit;
  font-weight: 600;
  border-radius: 8px;
  cursor: pointer;
  transition: transform 0.1s, opacity 0.2s;
}
.btn:hover { transform: translateY(-1px); }
.btn:active { transform: translateY(0); }
.btn.ghost {
  background: transparent;
  color: var(--ink);
  border: 1px solid var(--line);
}

/* IP */
.ip-examples {
  display: flex; flex-wrap: wrap; gap: 12px;
  margin: 1em 0 2em;
}
.ip-pill {
  background: var(--panel);
  padding: 10px 18px;
  border-radius: 999px;
  font-family: "SF Mono", Menlo, monospace;
  border: 1px solid var(--line);
}
.ip-quiz {
  display: grid;
  gap: 14px;
  margin: 1em 0;
}
.ip-question {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 16px 20px;
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 14px;
  align-items: center;
  transition: border-color 0.25s, background 0.25s;
}
.ip-question.correct { border-color: var(--good); background: rgba(52,211,153,0.08); }
.ip-question.wrong   { border-color: var(--bad);  background: rgba(248,113,113,0.08); }
.ip-question .ip-value {
  font-family: "SF Mono", Menlo, monospace;
  font-size: 1.4rem;
  letter-spacing: 0.02em;
}
.ip-question .ip-buttons {
  display: flex; gap: 8px;
}
.ip-btn {
  background: transparent;
  color: var(--ink);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 8px 14px;
  font: inherit;
  font-size: 0.95rem;
  cursor: pointer;
  transition: all 0.15s;
}
.ip-btn:hover:not(:disabled) { border-color: var(--accent); }
.ip-btn:disabled { cursor: default; opacity: 0.65; }
.ip-btn.picked-correct { background: var(--good); color: var(--bg); border-color: var(--good); }
.ip-btn.picked-wrong   { background: var(--bad);  color: var(--bg); border-color: var(--bad); }
.ip-explain {
  grid-column: 1 / -1;
  margin: 0;
  color: var(--ink-dim);
  font-size: 0.92rem;
  display: none;
}
.ip-question.answered .ip-explain { display: block; }

/* DNS */
.dns-stage {
  display: grid;
  grid-template-columns: 1fr 2fr 1fr;
  align-items: center;
  gap: 20px;
  margin: 2em 0;
  background: var(--panel);
  padding: 30px 20px;
  border-radius: var(--radius);
  border: 1px solid var(--line);
}
.dns-node {
  text-align: center;
}
.node-emoji { font-size: 3rem; }
.node-label { color: var(--ink-dim); font-size: 0.95rem; margin-top: 6px; }
.dns-wire {
  position: relative;
  height: 60px;
  border-top: 2px dashed rgba(255,255,255,0.2);
  border-bottom: 2px dashed rgba(255,255,255,0.2);
}
.dns-msg {
  position: absolute;
  top: 50%;
  left: 0;
  transform: translate(-50%, -50%);
  background: var(--accent-2);
  color: white;
  padding: 6px 14px;
  border-radius: 999px;
  font-size: 0.85rem;
  font-family: "SF Mono", Menlo, monospace;
  white-space: nowrap;
  opacity: 0;
  pointer-events: none;
  transition: left 2.5s ease-in-out, opacity 0.3s, background 0.3s;
}
.dns-msg.visible { opacity: 1; }
.dns-msg.reply { background: var(--good); }
.dns-controls {
  display: flex; gap: 10px; margin: 1em 0;
}
.dns-controls input {
  flex: 1;
  min-width: 0;
  background: var(--panel);
  color: var(--ink);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 12px 16px;
  font: inherit;
}

/* Packets */
.mode-tabs {
  display: flex; gap: 8px; flex-wrap: wrap;
  margin: 1em 0;
}
.mode-tab {
  background: var(--panel);
  color: var(--ink-dim);
  border: 1px solid var(--line);
  padding: 10px 16px;
  border-radius: 999px;
  cursor: pointer;
  font: inherit;
  font-size: 0.95rem;
  transition: all 0.15s;
}
.mode-tab:hover { color: var(--ink); border-color: var(--accent); }
.mode-tab.active {
  background: var(--accent);
  color: var(--bg);
  border-color: var(--accent);
  font-weight: 600;
}

.packet-controls {
  display: flex; gap: 10px; margin: 1em 0;
  align-items: center;
  flex-wrap: wrap;
}
.packet-controls[hidden] { display: none; }
.packet-controls .route-info {
  flex: 1 1 100%;
  margin: 0;
  color: var(--ink-dim);
  font-size: 0.95rem;
  line-height: 1.5;
}
.packet-controls input {
  flex: 1;
  background: var(--panel);
  color: var(--ink);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 12px 16px;
  font: inherit;
}
.packet-stage {
  position: relative;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 20px;
  margin: 1em 0;
  display: grid;
  grid-template-columns: 100px 1fr 100px;
  align-items: center;
  gap: 10px;
  min-height: 240px;
  overflow: hidden;
}
.packet-endpoint { text-align: center; z-index: 2; }
.packet-routes {
  position: relative;
  height: 200px;
}
.route {
  position: absolute;
  left: 0; right: 0;
  height: 2px;
  background: rgba(255,255,255,0.12);
  border-radius: 2px;
  transition: background 0.3s;
}
.route-top { top: 25px; }
.route-mid { top: 50%; transform: translateY(-1px); }
.route-bot { bottom: 25px; }
.route.slow { background: rgba(251,191,36,0.5); }
.route.down { background: rgba(248,113,113,0.4); border-top: 2px dashed rgba(248,113,113,0.6); height: 0; }
.route.fast { background: rgba(52,211,153,0.6); }
.route-label {
  position: absolute;
  right: 10px; top: -22px;
  font-size: 0.8rem;
  padding: 2px 8px;
  border-radius: 4px;
  background: var(--panel);
  color: var(--ink-dim);
  white-space: nowrap;
}
.route-label.slow { color: var(--warn); border: 1px solid rgba(251,191,36,0.5); }
.route-label.down { color: var(--bad); border: 1px solid rgba(248,113,113,0.5); }
.route-label.fast { color: var(--good); border: 1px solid rgba(52,211,153,0.5); }
.packet-layer {
  position: absolute;
  inset: 0;
  pointer-events: none;
  z-index: 2;
}

/* Network view (fastest-route mode) */
#network-view {
  position: absolute;
  inset: 0;
  z-index: 1;
}
#network-view svg {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  pointer-events: none;
}
.net-node {
  position: absolute;
  transform: translate(-50%, -50%);
  text-align: center;
  pointer-events: none;
}
.net-emoji {
  background: var(--panel);
  border: 2px solid var(--accent);
  width: 46px; height: 46px;
  border-radius: 50%;
  display: flex; align-items: center; justify-content: center;
  margin: 0 auto;
  font-size: 1.4rem;
  box-shadow: 0 2px 10px rgba(0,0,0,0.4);
  transition: box-shadow 0.2s, transform 0.2s;
}
.net-node-router .net-emoji {
  font-size: 1.1rem;
  width: 38px; height: 38px;
  border-color: var(--accent-2);
  background: #243057;
}
.net-label {
  font-size: 0.72rem;
  color: var(--ink-dim);
  margin-top: 4px;
  white-space: nowrap;
}
.net-node.thinking .net-emoji {
  box-shadow: 0 0 0 6px rgba(94,234,212,0.35);
  transform: scale(1.15);
}
.net-edge-label {
  font-family: -apple-system, sans-serif;
  font-weight: 600;
  paint-order: stroke;
  stroke: #0f172a;
  stroke-width: 3px;
}
.packet-stage.route-mode .packet-endpoint,
.packet-stage.route-mode .packet-routes {
  display: none;
}
.packet-stage.route-mode {
  grid-template-columns: 1fr;
}
.packet {
  position: absolute;
  background: var(--accent);
  color: var(--bg);
  border-radius: 6px;
  padding: 4px 8px;
  font-family: "SF Mono", Menlo, monospace;
  font-size: 0.85rem;
  font-weight: 600;
  white-space: nowrap;
  transform: translate(-50%, -50%);
  box-shadow: 0 4px 12px rgba(94,234,212,0.4);
  transition: left 2s ease-in-out, top 2s ease-in-out, opacity 0.3s;
}
.packet-output {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 20px;
  margin-top: 1em;
}
.po-block {
  background: var(--panel);
  padding: 16px;
  border-radius: var(--radius);
  border: 1px solid var(--line);
  min-height: 100px;
}
.po-block h4 { margin: 0 0 10px; color: var(--ink-dim); font-size: 0.9rem; text-transform: uppercase; letter-spacing: 0.08em; }
.packet-list {
  display: flex; flex-wrap: wrap; gap: 6px;
}
.packet-list .arrived {
  background: var(--accent);
  color: var(--bg);
  padding: 4px 10px;
  border-radius: 6px;
  font-family: "SF Mono", Menlo, monospace;
  font-size: 0.85rem;
  font-weight: 600;
  animation: pop 0.3s;
}
@keyframes pop {
  0% { transform: scale(0.5); opacity: 0; }
  100% { transform: scale(1); opacity: 1; }
}
.packet-final {
  font-family: "SF Mono", Menlo, monospace;
  font-size: 1.1rem;
  letter-spacing: 0.05em;
  word-break: break-all;
  min-height: 1.5em;
}
.packet-final-image {
  display: flex;
  flex-direction: row;
  gap: 0;
  min-height: 100px;
  align-items: center;
  justify-content: center;
}
.image-strip {
  height: 100px;
  width: 30px;
  background-size: 180px 100px;
  background-repeat: no-repeat;
  opacity: 0;
  transition: opacity 0.3s;
}
.image-strip.visible { opacity: 1; }
.packet.image-packet {
  padding: 0;
  background: transparent;
  box-shadow: 0 4px 12px rgba(0,0,0,0.3);
  border: 2px solid var(--accent);
  border-radius: 4px;
  overflow: hidden;
}
.packet.image-packet .packet-num {
  position: absolute;
  top: -8px; left: -8px;
  background: var(--accent);
  color: var(--bg);
  font-size: 0.7rem;
  font-weight: 700;
  padding: 1px 5px;
  border-radius: 4px;
  font-family: "SF Mono", Menlo, monospace;
}
.packet.image-packet .packet-strip {
  height: 40px;
  width: 22px;
  background-size: 132px 40px;
  background-repeat: no-repeat;
}
.packet-list .arrived.image-arrived {
  padding: 0;
  background: transparent;
  border: 1px solid var(--accent);
  position: relative;
  overflow: visible;
}
.packet-list .arrived.image-arrived .mini-strip {
  height: 30px; width: 18px;
  background-size: 108px 30px;
  background-repeat: no-repeat;
}
.packet-list .arrived.image-arrived .mini-num {
  position: absolute;
  bottom: -16px;
  left: 50%;
  transform: translateX(-50%);
  font-size: 0.7rem;
  color: var(--ink-dim);
  font-family: "SF Mono", Menlo, monospace;
}

/* Plenary */
.term-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 16px;
  margin: 1.5em 0;
}
.end-note {
  text-align: center;
  font-size: 1.3rem;
  margin-top: 3em;
  color: var(--accent);
}

/* Responsive */
@media (max-width: 800px) {
  #side-nav { display: none; }
  .section { padding: 60px 18px; }
  .tld-game { grid-template-columns: 1fr; }
  .dns-stage { grid-template-columns: 1fr; gap: 16px; }
  .dns-wire { display: none; }
  .packet-stage { grid-template-columns: 60px 1fr 60px; }
  .packet-output { grid-template-columns: 1fr; }
  .node-emoji { font-size: 2rem; }
}