:root {
  color-scheme: dark;
  --bg: #07131d;
  --bg-soft: #0b1d2a;
  --card: rgba(15, 34, 47, .92);
  --card-2: #102a3a;
  --line: #244556;
  --line-soft: rgba(137, 196, 214, .14);
  --text: #e8f3f4;
  --muted: #91acb5;
  --faint: #62808b;
  --cyan: #58d4dc;
  --cyan-2: #2caebc;
  --green: #77e1ac;
  --amber: #f1bd6b;
  --red: #ff807b;
  --shadow: 0 20px 55px rgba(0, 0, 0, .24);
  --radius: 18px;
}

@media (prefers-color-scheme: light) {
  :root {
    color-scheme: light;
    --bg: #eef5f6;
    --bg-soft: #e3eff1;
    --card: rgba(255, 255, 255, .94);
    --card-2: #f6fbfb;
    --line: #cbdde0;
    --line-soft: rgba(27, 77, 89, .14);
    --text: #15313b;
    --muted: #58737b;
    --faint: #7a979e;
    --cyan: #078b9c;
    --cyan-2: #057182;
    --green: #178859;
    --amber: #ad6b13;
    --red: #bd403c;
    --shadow: 0 18px 40px rgba(22, 68, 79, .13);
  }
}

html[data-theme="dark"] {
  color-scheme: dark;
  --bg: #07131d;
  --bg-soft: #0b1d2a;
  --card: rgba(15, 34, 47, .92);
  --card-2: #102a3a;
  --line: #244556;
  --line-soft: rgba(137, 196, 214, .14);
  --text: #e8f3f4;
  --muted: #91acb5;
  --faint: #62808b;
  --cyan: #58d4dc;
  --cyan-2: #2caebc;
  --green: #77e1ac;
  --amber: #f1bd6b;
  --red: #ff807b;
}

html[data-theme="light"] {
  color-scheme: light;
  --bg: #eef5f6;
  --bg-soft: #e3eff1;
  --card: rgba(255, 255, 255, .94);
  --card-2: #f6fbfb;
  --line: #cbdde0;
  --line-soft: rgba(27, 77, 89, .14);
  --text: #15313b;
  --muted: #58737b;
  --faint: #7a979e;
  --cyan: #078b9c;
  --cyan-2: #057182;
  --green: #178859;
  --amber: #ad6b13;
  --red: #bd403c;
}

* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; min-height: 100%; }
body {
  min-height: 100dvh;
  overflow: hidden;
  background:
    radial-gradient(circle at 10% 0%, rgba(30, 112, 131, .18), transparent 35rem),
    var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  touch-action: manipulation;
}

button {
  min-height: 44px;
  border: 1px solid var(--line);
  border-radius: 11px;
  background: var(--card-2);
  color: var(--text);
  font: inherit;
  cursor: pointer;
  transition: background .2s ease, border-color .2s ease, color .2s ease, transform .2s ease, box-shadow .2s ease;
}
button:hover { border-color: var(--cyan); color: var(--cyan); transform: translateY(-1px); }
button:active { transform: translateY(0); }
button:focus-visible, [tabindex="0"]:focus-visible { outline: 3px solid rgba(88, 212, 220, .38); outline-offset: 3px; }
button:disabled { opacity: .42; cursor: not-allowed; transform: none; }

.shell {
  width: min(1500px, 100%);
  height: 100dvh;
  margin: 0 auto;
  padding: 24px clamp(16px, 3vw, 44px) calc(68px + env(safe-area-inset-bottom));
  overflow: auto;
  scrollbar-width: thin;
  scrollbar-color: var(--line) transparent;
}

.topbar, .intro-row, .card-heading, .section-top, .packet-top, .progress-foot {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 18px;
}

.topbar {
  padding-bottom: 22px;
  border-bottom: 1px solid var(--line-soft);
}
.brand { display: flex; align-items: center; gap: 14px; }
.brand-mark {
  width: 46px; height: 46px; border: 1px solid var(--cyan);
  border-radius: 14px; display: grid; place-content: center; gap: 4px;
  background: rgba(88, 212, 220, .08);
  box-shadow: 0 0 30px rgba(88, 212, 220, .12);
}
.brand-mark span { display: block; height: 3px; border-radius: 3px; background: var(--cyan); }
.brand-mark span:nth-child(1) { width: 20px; }
.brand-mark span:nth-child(2) { width: 13px; margin-left: 7px; background: var(--green); }
.brand-mark span:nth-child(3) { width: 20px; }

h1, h2, h3, p { margin: 0; }
h1 { font-size: clamp(1.05rem, 2vw, 1.35rem); letter-spacing: -.03em; }
h2 { font-size: clamp(1.45rem, 3vw, 2.35rem); letter-spacing: -.045em; margin: 7px 0 10px; }
h3 { font-size: 1.12rem; letter-spacing: -.02em; }
.eyebrow, .section-label {
  color: var(--cyan); font-size: .68rem; font-weight: 800;
  letter-spacing: .13em; text-transform: uppercase;
}
.intro-row { align-items: flex-end; padding: 28px 0 24px; }
.intro-copy { max-width: 720px; }
.intro-copy > p:last-child { color: var(--muted); line-height: 1.55; }
.scenario-controls { display: flex; flex-wrap: wrap; justify-content: flex-end; gap: 8px; }
.scenario, .reset-button { padding: 0 13px; font-size: .78rem; white-space: nowrap; }
.scenario b { color: var(--faint); margin-left: 7px; font-size: .66rem; }
.scenario.active { background: rgba(88, 212, 220, .14); border-color: var(--cyan); }
.scenario.active b { color: var(--green); }
.reset-button { color: var(--muted); }

.workspace { display: grid; grid-template-columns: minmax(0, 1.55fr) minmax(285px, .7fr); gap: 16px; }
.card {
  background: linear-gradient(145deg, var(--card), color-mix(in srgb, var(--card) 78%, var(--bg)));
  border: 1px solid var(--line-soft);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}
.map-card { min-width: 0; padding: 20px; }
.card-heading { align-items: flex-start; }
.card-heading.compact { align-items: center; }
.route-readout { color: var(--faint); font-size: .63rem; letter-spacing: .1em; text-align: right; }
.route-readout strong { display: block; color: var(--cyan); font-size: .72rem; letter-spacing: .03em; margin-top: 5px; }
.map-wrap { position: relative; margin-top: 16px; border-radius: 14px; overflow: hidden; background: #102a3d; }
#networkMap { display: block; width: 100%; height: auto; min-height: 240px; }
.shore { fill: #1a5260; opacity: .7; }
.map-help {
  position: absolute; left: 14px; bottom: 12px; padding: 7px 10px;
  color: #b6d4d8; background: rgba(4, 19, 28, .7); border: 1px solid rgba(150, 220, 226, .18);
  border-radius: 8px; font-size: .7rem;
}
.edge { stroke: #4e7580; stroke-width: 8; opacity: .65; cursor: pointer; transition: stroke .2s, opacity .2s; }
.edge:hover, .edge:focus { stroke: #b6e6df; opacity: 1; outline: none; }
.edge.active { stroke: var(--green); opacity: 1; filter: drop-shadow(0 0 5px rgba(119, 225, 172, .6)); }
.node { cursor: pointer; }
.node circle { stroke: rgba(255,255,255,.2); stroke-width: 2; transition: transform .2s, stroke .2s; }
.node > circle:first-child { fill: rgba(15, 36, 48, .95); }
.node-core { fill: #193c4d; }
.node text { fill: white; font-size: 21px; font-weight: 800; text-anchor: middle; pointer-events: none; }
.node .node-label { font-size: 15px; letter-spacing: .04em; }
.node.client .node-core { fill: #236176; }
.node.router .node-core { fill: #236e69; }
.node.firewall .node-core { fill: #785c32; }
.node.relay .node-core { fill: #55518b; }
.node.server .node-core { fill: #286c58; }
.node.keyboard-focus circle:first-child, .node:hover circle:first-child { stroke: var(--cyan); stroke-width: 4; }
.trace-chips { display: flex; flex-wrap: wrap; gap: 7px; margin-top: 14px; }
.trace-chip { padding: 7px 10px; background: rgba(119, 225, 172, .1); color: var(--green); border: 1px solid rgba(119, 225, 172, .25); border-radius: 999px; font-size: .72rem; }
.trace-chip b { color: var(--faint); margin-right: 6px; }

.side-column { display: flex; flex-direction: column; gap: 16px; min-width: 0; }
.inspector, .progress-card, .events { padding: 18px; }
.packet-id { color: var(--cyan); font-weight: 800; font-size: .85rem; }
.inspector h3 { margin: 15px 0; line-height: 1.4; }
dl { margin: 0; display: grid; gap: 9px; }
dl div { display: flex; justify-content: space-between; gap: 12px; border-bottom: 1px solid var(--line-soft); padding-bottom: 8px; }
dt { color: var(--muted); font-size: .75rem; }
dd { margin: 0; font-size: .78rem; font-weight: 700; }
.good-text { color: var(--green); }
.bad-text, .bad { color: var(--red) !important; }
.safe-callout, .repair-callout { margin-top: 15px; padding: 12px; border-radius: 11px; font-size: .76rem; }
.safe-callout { background: rgba(119, 225, 172, .1); color: var(--green); border: 1px solid rgba(119, 225, 172, .24); }
.repair-callout { display: grid; gap: 5px; background: rgba(255, 128, 123, .09); border: 1px solid rgba(255, 128, 123, .28); }
.repair-callout span, .inspector-hint { color: var(--muted); }
.repair-button { color: var(--amber); border-color: rgba(241, 189, 107, .35); }
.wide { width: 100%; margin-top: 8px; }
.progress-bar { height: 8px; overflow: hidden; margin: 15px 0 10px; border-radius: 99px; background: var(--line); }
.progress-bar span { display: block; height: 100%; border-radius: inherit; background: linear-gradient(90deg, var(--cyan), var(--green)); transition: width .4s ease; }
.progress-foot { color: var(--muted); font-size: .72rem; }
.events { min-height: 0; }
.panel-toggle { min-height: 34px; padding: 0 10px; font-size: .7rem; }
#eventBody { max-height: 225px; margin-top: 12px; overflow: auto; }
#eventBody.collapsed { display: none; }
.event { display: grid; grid-template-columns: 23px 1fr; gap: 8px; padding: 8px 0; border-top: 1px solid var(--line-soft); }
.event > span { color: var(--faint); font: .65rem ui-monospace, SFMono-Regular, Consolas, monospace; padding-top: 2px; }
.event p { color: var(--muted); font-size: .73rem; line-height: 1.35; }
.event.success p { color: var(--green); }
.event.error p { color: var(--red); }
.event.route p { color: var(--cyan); }
.event.repair p { color: var(--amber); }

.packet-section { padding-top: 22px; }
.section-top { align-items: flex-end; margin-bottom: 12px; }
.keyboard-note { color: var(--faint); font-size: .7rem; }
kbd { padding: 3px 6px; border: 1px solid var(--line); border-radius: 5px; color: var(--text); background: var(--card-2); }
.packet-grid { display: grid; grid-template-columns: repeat(4, minmax(0, 1fr)); gap: 12px; }
.packet { min-width: 0; padding: 15px; background: var(--card); border: 1px solid var(--line-soft); border-radius: 15px; transition: transform .2s, border-color .2s, box-shadow .2s; }
.packet:hover, .packet.selected { transform: translateY(-2px); border-color: var(--cyan); box-shadow: 0 12px 28px rgba(0,0,0,.15); }
.packet.delivered { border-color: rgba(119, 225, 172, .3); }
.packet.retry { border-color: rgba(255, 128, 123, .35); }
.packet-top { margin-bottom: 10px; }
.packet-identity { display: flex; align-items: center; gap: 9px; }
.packet-identity strong { font-size: .95rem; }
.packet-car { width: 34px; height: 34px; object-fit: contain; image-rendering: auto; filter: drop-shadow(0 3px 4px rgba(0,0,0,.35)); }
.status { padding: 4px 7px; border-radius: 99px; font-size: .58rem; font-weight: 800; letter-spacing: .06em; background: rgba(145, 172, 181, .12); color: var(--muted); }
.status.delivered { background: rgba(119, 225, 172, .12); color: var(--green); }
.status.retry { background: rgba(255, 128, 123, .12); color: var(--red); }
.status.transit { background: rgba(88, 212, 220, .12); color: var(--cyan); }
.packet > p { min-height: 42px; color: var(--muted); font-size: .76rem; line-height: 1.4; }
.header-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 8px; margin: 13px 0; }
.header-grid span { color: var(--faint); font-size: .58rem; letter-spacing: .08em; }
.header-grid strong { display: block; overflow: hidden; color: var(--text); font-size: .72rem; letter-spacing: 0; text-overflow: ellipsis; white-space: nowrap; margin-top: 3px; }
.packet-actions { display: grid; grid-template-columns: 1fr 1fr; gap: 6px; }
.packet-actions button { min-height: 38px; padding: 0 7px; font-size: .67rem; }
.packet-actions .dispatch-button { grid-column: span 2; color: var(--cyan); border-color: rgba(88,212,220,.35); }
.inspect-button { color: var(--muted); }

.quiz-backdrop { position: fixed; inset: 0; z-index: 5; display: grid; place-items: center; padding: 18px; background: rgba(2, 12, 19, .78); backdrop-filter: blur(9px); }
.quiz-backdrop[hidden] { display: none; }
.quiz-dialog { width: min(540px, 100%); padding: clamp(22px, 5vw, 38px); background: var(--card); border: 1px solid var(--cyan); border-radius: 20px; box-shadow: 0 30px 100px rgba(0,0,0,.45); }
.quiz-progress { color: var(--cyan); font-size: .68rem; font-weight: 800; letter-spacing: .12em; }
.quiz-dialog h2 { margin-top: 13px; }
.quiz-dialog > p { color: var(--muted); line-height: 1.5; }
.quiz-choices { display: grid; gap: 9px; margin-top: 22px; }
.choice { display: flex; align-items: center; gap: 12px; min-height: 52px; padding: 9px 13px; text-align: left; }
.choice:first-letter { color: var(--cyan); font-weight: 800; }
.choice span { font-size: .82rem; }
.quiz-footer { display: flex; justify-content: space-between; gap: 12px; margin-top: 22px; color: var(--faint); font-size: .72rem; }
.result-score { color: var(--green); font-size: 2.7rem; font-weight: 800; text-align: center; }

@media (max-width: 1120px) {
  .packet-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}
@media (max-width: 760px) {
  body { overflow: auto; }
  .shell { height: auto; min-height: 100dvh; }
  .topbar, .intro-row { align-items: flex-start; flex-direction: column; }
  .chapter-nav { width: 100%; display: grid; grid-template-columns: repeat(3, 1fr); }
  .chapter-tab { min-width: 0; padding: 0 4px; font-size: .68rem; }
  .scenario-controls { justify-content: flex-start; }
  .workspace { grid-template-columns: 1fr; }
  .side-column { display: grid; grid-template-columns: 1fr 1fr; }
  .inspector { grid-column: span 2; }
  .events { min-height: 210px; }
  .section-top { align-items: flex-start; flex-direction: column; }
}
@media (max-width: 470px) {
  .shell { padding: 15px 12px calc(68px + env(safe-area-inset-bottom)); }
  .map-card, .inspector, .progress-card, .events { padding: 14px; }
  .route-readout { display: none; }
  #networkMap { min-height: 190px; }
  .map-help { position: static; border: 0; border-radius: 0; font-size: .65rem; }
  .side-column, .packet-grid { grid-template-columns: 1fr; }
  .inspector { grid-column: auto; }
  .packet-grid { gap: 10px; }
  .keyboard-note { display: none; }
  .scenario-controls { width: 100%; }
  .scenario, .reset-button { flex: 1; padding: 0 7px; }
}