/* =====================================================================
   System Design Visualized: styles
   ===================================================================== */

:root {
  --bg: #0c0d11;
  --bg-2: #111318;
  --panel: #15171d;
  --panel-2: #1b1e26;
  --border: #272a34;
  --border-strong: #363a47;
  --text: #e8e9ed;
  --muted: #9a9fad;
  --accent: #7b7bf0;
  --accent-2: #4fb8c2;
  --accent-soft: #1f2036;
  --ok: #22c55e;
  --bad: #ef4444;
  --warn: #f59e0b;
  --code-bg: #101217;
  --shadow: 0 1px 2px rgba(0, 0, 0, 0.3);
  --shadow-lg: 0 16px 40px rgba(0, 0, 0, 0.45);
  --radius: 12px;
  --focus: 0 0 0 3px color-mix(in srgb, var(--accent) 35%, transparent);

  --k-client: #60a5fa;
  --k-server: #34d399;
  --k-db: #fbbf24;
  --k-cache: #f472b6;
  --k-lb: #a78bfa;
  --k-queue: #fb923c;
  --k-cdn: #2dd4bf;
  --k-service: #818cf8;
  --k-external: #94a3b8;
  --k-dns: #22d3ee;
  --k-storage: #facc15;
  --k-worker: #4ade80;
  --k-limiter: #f87171;

  --tok-k: #c792ea;
  --tok-s: #c3e88d;
  --tok-n: #f78c6c;
  --tok-c: #6b7599;
  --tok-f: #82aaff;

  color-scheme: dark;
}

@media (prefers-color-scheme: light) {
  :root:not([data-theme="dark"]) {
    --bg: #f7f7f9;
    --bg-2: #f0f1f4;
    --panel: #ffffff;
    --panel-2: #f6f7f9;
    --border: #e3e5ea;
    --border-strong: #cfd3db;
    --text: #16181d;
    --muted: #5f6573;
    --accent: #5b5bd6;
    --accent-2: #0e7c86;
    --accent-soft: #eeeefc;
    --code-bg: #f6f7f9;
    --shadow: 0 1px 2px rgba(16, 24, 40, 0.05), 0 1px 3px rgba(16, 24, 40, 0.04);
    --shadow-lg: 0 12px 32px rgba(16, 24, 40, 0.12);
    --k-client: #2563eb;
    --k-server: #059669;
    --k-db: #d97706;
    --k-cache: #db2777;
    --k-lb: #7c3aed;
    --k-queue: #ea580c;
    --k-cdn: #0d9488;
    --k-service: #4f46e5;
    --k-external: #64748b;
    --k-dns: #0891b2;
    --k-storage: #ca8a04;
    --k-worker: #16a34a;
    --k-limiter: #dc2626;
    --tok-k: #7c3aed;
    --tok-s: #15803d;
    --tok-n: #c2410c;
    --tok-c: #8a93b0;
    --tok-f: #2563eb;
    color-scheme: light;
  }
}

:root[data-theme="light"] {
  --bg: #f7f7f9;
  --bg-2: #f0f1f4;
  --panel: #ffffff;
  --panel-2: #f6f7f9;
  --border: #e3e5ea;
  --border-strong: #cfd3db;
  --text: #16181d;
  --muted: #5f6573;
  --accent: #5b5bd6;
  --accent-2: #0e7c86;
  --accent-soft: #eeeefc;
  --code-bg: #f6f7f9;
  --shadow: 0 1px 2px rgba(16, 24, 40, 0.05), 0 1px 3px rgba(16, 24, 40, 0.04);
  --shadow-lg: 0 12px 32px rgba(16, 24, 40, 0.12);
  --k-client: #2563eb;
  --k-server: #059669;
  --k-db: #d97706;
  --k-cache: #db2777;
  --k-lb: #7c3aed;
  --k-queue: #ea580c;
  --k-cdn: #0d9488;
  --k-service: #4f46e5;
  --k-external: #64748b;
  --k-dns: #0891b2;
  --k-storage: #ca8a04;
  --k-worker: #16a34a;
  --k-limiter: #dc2626;
  --tok-k: #7c3aed;
  --tok-s: #15803d;
  --tok-n: #c2410c;
  --tok-c: #8a93b0;
  --tok-f: #2563eb;
  color-scheme: light;
}

* {
  box-sizing: border-box;
}
/* the hidden attribute always wins over component display rules */
[hidden] {
  display: none !important;
}

html {
  scroll-padding-top: 124px;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font: 16px/1.65 Inter, system-ui, -apple-system, "Segoe UI", sans-serif;
  -webkit-font-smoothing: antialiased;
}

a {
  color: var(--accent);
}
:focus-visible {
  outline: none;
  box-shadow: var(--focus);
}

code,
kbd,
pre {
  font-family: "JetBrains Mono", ui-monospace, Consolas, monospace;
}

.muted {
  color: var(--muted);
}

/* ------------------------------------------------------------ buttons */
.btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  border: 1px solid var(--border);
  background: var(--panel-2);
  color: var(--text);
  padding: 7px 14px;
  border-radius: 9px;
  font: 600 14px/1.2 Inter, system-ui, sans-serif;
  cursor: pointer;
  text-decoration: none;
  white-space: nowrap;
  transition: background 0.15s, border-color 0.15s, color 0.15s, transform 0.08s;
}
.btn:hover:not(:disabled) {
  border-color: var(--border-strong);
  background: color-mix(in srgb, var(--text) 5%, var(--panel-2));
}
.btn:active:not(:disabled) {
  transform: scale(0.98);
}
.btn.loading {
  pointer-events: none;
  color: transparent !important;
  position: relative;
}
.btn.loading::after {
  content: "";
  position: absolute;
  inset: 0;
  margin: auto;
  width: 15px;
  height: 15px;
  border-radius: 50%;
  border: 2px solid currentColor;
  border-color: var(--muted) transparent var(--muted) transparent;
  animation: spin 0.7s linear infinite;
}
.btn.primary.loading::after {
  border-color: #fff transparent #fff transparent;
}
@keyframes spin {
  to {
    transform: rotate(360deg);
  }
}
.btn.ghost {
  background: transparent;
  border-color: transparent;
}
.btn.danger-text {
  color: var(--bad);
}
.btn.small {
  padding: 5px 10px;
  font-size: 13px;
  border-radius: 8px;
}
.btn:disabled {
  opacity: 0.45;
  cursor: not-allowed;
}
.btn.primary {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
}
.btn.primary:hover:not(:disabled) {
  background: color-mix(in srgb, var(--accent) 88%, #000);
  border-color: color-mix(in srgb, var(--accent) 88%, #000);
}
.btn.big {
  padding: 12px 20px;
  font-size: 15px;
  border-radius: 12px;
}
.btn.icon {
  padding: 7px 10px;
}
.btn kbd {
  font-size: 11px;
  opacity: 0.75;
  font-weight: 400;
}
.btn.ctrl {
  background: var(--panel);
}
.btn.ctrl.danger {
  border-color: color-mix(in srgb, var(--bad) 40%, var(--border));
}
.btn.ctrl.good {
  border-color: color-mix(in srgb, var(--ok) 40%, var(--border));
}

.pill {
  display: inline-block;
  padding: 4px 12px;
  border-radius: 99px;
  font-size: 13px;
  font-weight: 600;
  color: var(--accent);
  background: var(--accent-soft);
  border: 1px solid color-mix(in srgb, var(--accent) 22%, transparent);
}

/* ------------------------------------------------------------ top bar */
.topbar {
  position: sticky;
  top: 0;
  z-index: 30;
  height: 60px;
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 0 18px;
  background: color-mix(in srgb, var(--bg) 82%, transparent);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
}
.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  color: var(--text);
  text-decoration: none;
  font-weight: 800;
  font-size: 17px;
  letter-spacing: -0.01em;
  white-space: nowrap;
}
.brand em {
  font-style: normal;
  color: var(--accent);
}
.brand-logo {
  font-size: 22px;
}
.spacer {
  flex: 1;
}
.menu-btn {
  display: none;
}
.xp {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 13px;
  font-weight: 700;
  color: var(--muted);
}
.xp-bar {
  width: 120px;
  height: 8px;
  border-radius: 99px;
  background: var(--panel-2);
  border: 1px solid var(--border);
  overflow: hidden;
}
.xp-bar span {
  display: block;
  height: 100%;
  width: 0;
  background: var(--accent);
  transition: width 0.6s;
}

/* ------------------------------------------------------------ layout */
.layout {
  display: grid;
  grid-template-columns: 290px minmax(0, 1fr);
}
.sidebar {
  position: sticky;
  top: 60px;
  height: calc(100vh - 60px);
  overflow-y: auto;
  padding: 16px 12px 40px;
  border-right: 1px solid var(--border);
  background: color-mix(in srgb, var(--bg-2) 60%, transparent);
}
.side-home {
  display: block;
  padding: 8px 12px;
  border-radius: 10px;
  color: var(--text);
  text-decoration: none;
  font-weight: 600;
  margin-bottom: 8px;
}
.side-home.active,
.side-home:hover {
  background: var(--panel-2);
}
.side-part {
  font-size: 11px;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--muted);
  font-weight: 700;
  margin: 18px 12px 6px;
}
.side-item {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 7px 10px;
  border-radius: 10px;
  color: var(--text);
  text-decoration: none;
  font-size: 14px;
  line-height: 1.3;
}
.side-item:hover {
  background: var(--panel-2);
}
.side-item.active {
  background: var(--accent-soft);
  box-shadow: inset 2px 0 0 var(--accent);
}
.side-num {
  --p: 0;
  flex: none;
  width: 28px;
  height: 28px;
  border-radius: 50%;
  display: grid;
  place-items: center;
  font-size: 12px;
  font-weight: 700;
  background: radial-gradient(closest-side, var(--panel) 76%, transparent 78% 100%),
    conic-gradient(var(--accent-2) calc(var(--p) * 1%), var(--border) 0);
}
.side-num.complete {
  background: var(--ok);
  color: #fff;
}

main {
  min-width: 0;
  outline: none;
}
.page {
  max-width: 1020px;
  margin: 0 auto;
  padding: 32px 28px 80px;
}

/* ------------------------------------------------------------ home */
.hero {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 28px;
  align-items: center;
  margin: 12px 0 34px;
}
.hero h1 {
  font-size: clamp(32px, 4.6vw, 50px);
  line-height: 1.08;
  letter-spacing: -0.03em;
  margin: 16px 0 14px;
}
.grad {
  color: var(--accent);
}
.lead {
  font-size: 17px;
  color: var(--muted);
}
.hero-cta {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
  margin-top: 22px;
}
.hero-anim {
  border-radius: 18px;
  border: 1px solid var(--border);
  background: var(--panel);
  box-shadow: var(--shadow);
  overflow: hidden;
}
.how {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 14px;
  margin-bottom: 40px;
}
.how-card {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 18px;
}
.how-card span {
  font-size: 22px;
  font-weight: 800;
  color: var(--accent-2);
}
.how-card h3 {
  margin: 6px 0 4px;
}
.how-card p {
  margin: 0;
  font-size: 14px;
  color: var(--muted);
}
.part h2 {
  margin: 34px 0 2px;
}
.part > p {
  margin: 0 0 14px;
}
.grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(230px, 1fr));
  gap: 14px;
}
.ch-card {
  position: relative;
  display: flex;
  flex-direction: column;
  gap: 4px;
  padding: 18px;
  border-radius: 16px;
  background: var(--panel);
  border: 1px solid var(--border);
  color: var(--text);
  text-decoration: none;
  transition: border-color 0.15s, background 0.15s;
  overflow: hidden;
}
.ch-card:hover {
  border-color: var(--border-strong);
  background: color-mix(in srgb, var(--text) 2%, var(--panel));
}
.ch-icon {
  font-size: 28px;
}
.ch-icon.big {
  font-size: 40px;
}
.ch-num {
  font-size: 12px;
  font-weight: 700;
  color: var(--accent-2);
  text-transform: uppercase;
  letter-spacing: 0.08em;
}
.ch-title {
  font-weight: 700;
  font-size: 17px;
  line-height: 1.3;
}
.ch-short {
  font-size: 14px;
  color: var(--muted);
  flex: 1;
}
.ch-meta {
  font-size: 12px;
  color: var(--muted);
  margin-top: 6px;
}
.ch-meta b {
  color: var(--accent-2);
}
.ch-meta b.ok {
  color: var(--ok);
}
.mini-bar {
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  height: 3px;
  background: transparent;
}
.mini-bar span {
  display: block;
  height: 100%;
  background: var(--accent);
}
.tips {
  margin-top: 40px;
}
.tips li {
  margin: 6px 0;
}

/* ------------------------------------------------------------ chapter */
.ch-head {
  margin-bottom: 18px;
}
.ch-head-top {
  display: flex;
  align-items: center;
  gap: 12px;
}
.ch-head h1 {
  font-size: clamp(28px, 4vw, 42px);
  letter-spacing: -0.025em;
  line-height: 1.12;
  margin: 12px 0 8px;
}
.ch-progress {
  height: 6px;
  border-radius: 99px;
  background: var(--panel-2);
  overflow: hidden;
  margin-top: 16px;
}
.ch-progress span {
  display: block;
  height: 100%;
  width: 0;
  background: var(--accent);
  transition: width 0.6s;
}
.toc {
  position: sticky;
  top: 60px;
  z-index: 10;
  display: flex;
  gap: 8px;
  overflow-x: auto;
  padding: 10px 0;
  margin-bottom: 14px;
  background: color-mix(in srgb, var(--bg) 88%, transparent);
  backdrop-filter: blur(10px);
  scrollbar-width: thin;
}
.toc a {
  flex: none;
  padding: 6px 12px;
  border-radius: 99px;
  border: 1px solid var(--border);
  background: var(--panel);
  color: var(--text);
  text-decoration: none;
  font-size: 13px;
  white-space: nowrap;
}
.toc a:hover {
  border-color: var(--border-strong);
}
.toc a b {
  color: var(--accent);
  margin-right: 2px;
}

.card {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 24px;
  margin-bottom: 20px;
  box-shadow: var(--shadow);
}
.sec-head {
  display: flex;
  align-items: center;
  gap: 12px;
  flex-wrap: wrap;
}
.sec-head h2 {
  margin: 0;
  font-size: 23px;
  letter-spacing: -0.015em;
  flex: 1;
  min-width: 200px;
}
.sec-num {
  flex: none;
  display: grid;
  place-items: center;
  min-width: 44px;
  height: 32px;
  padding: 0 8px;
  border-radius: 10px;
  font-weight: 800;
  font-size: 14px;
  color: var(--accent);
  background: var(--accent-soft);
}
.got-it {
  border: 1px solid var(--border);
  background: transparent;
  color: var(--muted);
  padding: 6px 12px;
  border-radius: 99px;
  font: 600 13px Inter, sans-serif;
  cursor: pointer;
}
.got-it:hover {
  border-color: var(--ok);
  color: var(--text);
}
.got-it.done {
  background: color-mix(in srgb, var(--ok) 18%, transparent);
  border-color: var(--ok);
  color: var(--ok);
}

.prose {
  font-size: 16px;
}
.prose p {
  margin: 12px 0;
}
.prose h3 {
  margin: 22px 0 6px;
  font-size: 18px;
}
.prose ul,
.prose ol {
  padding-left: 22px;
}
.prose li {
  margin: 5px 0;
}
.prose code {
  font-size: 0.88em;
  padding: 2px 6px;
  border-radius: 6px;
  background: var(--code-bg);
  border: 1px solid var(--border);
}
.prose pre {
  background: var(--code-bg);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 14px 16px;
  overflow-x: auto;
  font-size: 13.5px;
  line-height: 1.55;
}
.prose pre code {
  padding: 0;
  border: 0;
  background: none;
}
.prose table {
  width: 100%;
  border-collapse: collapse;
  font-size: 14.5px;
  margin: 14px 0;
  display: block;
  overflow-x: auto;
}
.prose th,
.prose td {
  text-align: left;
  padding: 8px 12px;
  border-bottom: 1px solid var(--border);
  vertical-align: top;
}
.prose th {
  color: var(--muted);
  font-size: 12.5px;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}
.prose b,
.prose strong {
  color: color-mix(in srgb, var(--text) 100%, var(--accent-2) 0%);
}
.callout {
  border-left: 4px solid var(--accent-2);
  background: color-mix(in srgb, var(--accent-2) 8%, transparent);
  padding: 12px 16px;
  border-radius: 0 12px 12px 0;
  margin: 14px 0;
}
.callout.warn {
  border-color: var(--warn);
  background: color-mix(in srgb, var(--warn) 9%, transparent);
}
.callout.analogy {
  border-color: var(--accent);
  background: color-mix(in srgb, var(--accent) 10%, transparent);
}
.callout > :first-child {
  margin-top: 0;
}
.callout > :last-child {
  margin-bottom: 0;
}
.lead.prose p {
  margin: 6px 0;
}

.compare {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 14px;
  margin: 14px 0;
}
.compare > div {
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 14px 16px;
  background: var(--panel-2);
}
.compare h4 {
  margin: 0 0 6px;
}
.compare ul {
  margin: 0;
  padding-left: 18px;
}

.keypoints {
  margin-top: 18px;
  border: 1px solid var(--border);
  border-left: 3px solid var(--accent);
  border-radius: 10px;
  padding: 12px 18px;
  background: var(--panel-2);
}
.keypoints h4 {
  margin: 2px 0 4px;
  font-size: 14px;
}
.keypoints ul {
  margin: 0;
  padding-left: 20px;
  font-size: 15px;
}

/* ------------------------------------------------------------ tabs */
.tabs {
  display: flex;
  gap: 6px;
  margin: 20px 0 0;
  border-bottom: 1px solid var(--border);
}
.tab {
  border: 1px solid transparent;
  border-bottom: none;
  background: none;
  color: var(--muted);
  padding: 9px 16px;
  border-radius: 12px 12px 0 0;
  font: 700 14px Inter, sans-serif;
  cursor: pointer;
  margin-bottom: -1px;
}
.tab.active {
  color: var(--text);
  background: var(--panel-2);
  border-color: var(--border);
}
.tab-panel {
  border: 1px solid var(--border);
  border-top: none;
  border-radius: 0 0 14px 14px;
  background: var(--panel-2);
  padding: 14px;
}

/* ------------------------------------------------------------ scene */
.stage-wrap {
  border-radius: 12px;
  background-color: var(--bg-2);
  background-image: radial-gradient(color-mix(in srgb, var(--muted) 22%, transparent) 1px, transparent 1px);
  background-size: 22px 22px;
  border: 1px solid var(--border);
  overflow: hidden;
}
.stage-svg {
  display: block;
  width: 100%;
  height: auto;
  max-height: min(60vh, 470px);
  font-family: Inter, system-ui, sans-serif;
}
.narration {
  display: flex;
  gap: 12px;
  align-items: flex-start;
  min-height: 62px;
  margin: 12px 0 10px;
  padding: 12px 14px;
  border-radius: 12px;
  background: var(--panel);
  border: 1px solid var(--border);
}
.step-count {
  flex: none;
  font-size: 12px;
  font-weight: 800;
  color: var(--accent-2);
  background: color-mix(in srgb, var(--accent-2) 12%, transparent);
  padding: 3px 9px;
  border-radius: 99px;
  margin-top: 2px;
}
.step-count:empty {
  display: none;
}
.narr-text {
  font-size: 15.5px;
}
.narr-text.fade {
  animation: fadeUp 0.35s ease;
}
@keyframes fadeUp {
  from {
    opacity: 0;
    transform: translateY(4px);
  }
}
.narr-text code {
  font-size: 0.88em;
  padding: 1px 5px;
  border-radius: 5px;
  background: var(--code-bg);
}
.transport {
  display: flex;
  gap: 8px;
  align-items: center;
  flex-wrap: wrap;
}
.transport.only-restart [data-a="prev"],
.transport.only-restart [data-a="play"],
.transport.only-restart [data-a="next"] {
  display: none;
}
.speed {
  font-size: 13px;
  color: var(--muted);
  display: flex;
  gap: 6px;
  align-items: center;
}
.speed select {
  background: var(--panel);
  color: var(--text);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 4px 6px;
}
.controls-title {
  font-size: 13px;
  font-weight: 700;
  color: var(--muted);
  margin: 14px 0 8px;
}
.controls-row {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
}
.scene-log {
  display: none;
  margin-top: 12px;
  padding: 10px 12px;
  border-radius: 10px;
  background: var(--code-bg);
  border: 1px solid var(--border);
  font: 12.5px/1.6 "JetBrains Mono", monospace;
  max-height: 190px;
  overflow: auto;
}
.scene-log.on {
  display: block;
}
.log-line {
  animation: fadeUp 0.25s ease;
}
.log-line.ok {
  color: var(--ok);
}
.log-line.bad {
  color: var(--bad);
}
.log-line.warn {
  color: var(--warn);
}
.log-line.info {
  color: var(--accent-2);
}

/* SVG: nodes */
.node {
  transition: opacity 0.5s;
}
.node.hidden,
.link.hidden,
.link-label.hidden {
  opacity: 0;
  pointer-events: none;
}
.node {
  --k: var(--k-server);
}
.kind-client { --k: var(--k-client); }
.kind-server { --k: var(--k-server); }
.kind-db { --k: var(--k-db); }
.kind-cache { --k: var(--k-cache); }
.kind-lb { --k: var(--k-lb); }
.kind-queue { --k: var(--k-queue); }
.kind-cdn { --k: var(--k-cdn); }
.kind-service { --k: var(--k-service); }
.kind-external { --k: var(--k-external); }
.kind-dns { --k: var(--k-dns); }
.kind-storage { --k: var(--k-storage); }
.kind-worker { --k: var(--k-worker); }
.kind-limiter { --k: var(--k-limiter); }

.node-box {
  fill: color-mix(in srgb, var(--k) 13%, var(--panel));
  stroke: var(--k);
  stroke-width: 2;
  transition: stroke 0.3s, fill 0.3s, stroke-width 0.3s;
}
.node-icon {
  font-size: 22px;
}
.node-icon.small {
  font-size: 16px;
}
.node-glyph {
  fill: none;
  stroke: var(--k);
  stroke-width: 1.8;
  stroke-linecap: round;
  stroke-linejoin: round;
  transition: stroke 0.3s;
}
.node.st-down .node-glyph,
.node.st-hot .node-glyph {
  stroke: var(--bad);
}
.node.st-ok .node-glyph {
  stroke: var(--ok);
}
.node.st-warn .node-glyph {
  stroke: var(--warn);
}
.node-label {
  fill: var(--text);
  font-size: 12.5px;
  font-weight: 700;
}
.node-sub {
  fill: var(--muted);
  font-size: 11px;
}
.node.hl .node-box {
  stroke-width: 3.5;
  fill: color-mix(in srgb, var(--k) 22%, var(--panel));
}
.node.pulse .node-box {
  animation: pulse 0.55s ease;
}
@keyframes pulse {
  0% {
    stroke-width: 2;
  }
  40% {
    stroke-width: 4.5;
  }
  100% {
    stroke-width: 2;
  }
}
.node.st-down {
  opacity: 0.45;
}
.node.st-down .node-box {
  stroke: var(--bad);
  stroke-dasharray: 6 4;
  fill: color-mix(in srgb, var(--bad) 10%, var(--panel));
}
.node.st-busy .node-box {
  animation: busy 0.7s ease-in-out infinite alternate;
}
@keyframes busy {
  to {
    fill: color-mix(in srgb, var(--warn) 30%, var(--panel));
    stroke: var(--warn);
  }
}
.node.st-hot .node-box {
  fill: color-mix(in srgb, var(--bad) 28%, var(--panel));
  stroke: var(--bad);
}
.node.st-ok .node-box {
  fill: color-mix(in srgb, var(--ok) 22%, var(--panel));
  stroke: var(--ok);
}
.node.st-warn .node-box {
  fill: color-mix(in srgb, var(--warn) 22%, var(--panel));
  stroke: var(--warn);
}
.badge rect {
  fill: var(--accent);
}
.badge text {
  fill: #fff;
  font-size: 11px;
  font-weight: 800;
}
.badge.bad rect {
  fill: var(--bad);
}
.badge.ok rect {
  fill: var(--ok);
}
.badge.warn rect {
  fill: var(--warn);
}

/* SVG: links */
.link {
  stroke: color-mix(in srgb, var(--muted) 55%, transparent);
  stroke-width: 2;
  transition: stroke 0.3s, opacity 0.5s;
}
.link.dashed {
  stroke-dasharray: 6 6;
}
.link.down {
  stroke: var(--bad);
  stroke-dasharray: 3 6;
  opacity: 0.5;
}
.link.active {
  stroke: var(--accent-2);
  stroke-width: 3;
}
.link.flow {
  stroke-dasharray: 8 8;
  animation: flow 0.8s linear infinite;
  stroke: var(--accent-2);
}
@keyframes flow {
  to {
    stroke-dashoffset: -16;
  }
}
.link-label {
  fill: var(--muted);
  font-size: 11px;
  paint-order: stroke;
  stroke: var(--bg-2);
  stroke-width: 4px;
}

/* SVG: packets */
.packet circle {
  fill: var(--pc);
  stroke: color-mix(in srgb, var(--pc) 55%, #000);
  stroke-width: 1;
}
.pkt-blue { --pc: #38bdf8; }
.pkt-green { --pc: #34d399; }
.pkt-red { --pc: #f87171; }
.pkt-amber { --pc: #fbbf24; }
.pkt-purple { --pc: #a78bfa; }
.pkt-pink { --pc: #f472b6; }
.pkt-gray { --pc: #94a3b8; }
.packet-label {
  fill: var(--text);
  font-size: 11.5px;
  font-weight: 700;
  paint-order: stroke;
  stroke: var(--bg-2);
  stroke-width: 4px;
}
.flash {
  font-size: 13px;
  font-weight: 800;
  fill: var(--accent-2);
  paint-order: stroke;
  stroke: var(--bg-2);
  stroke-width: 4px;
}
.flash.ok {
  fill: var(--ok);
}
.flash.bad {
  fill: var(--bad);
}
.flash.warn {
  fill: var(--warn);
}

/* SVG: free-form shapes used by custom scenes */
.st-text {
  fill: var(--text);
  font-size: 12.5px;
}
.st-text.muted {
  fill: var(--muted);
}
.st-text.small {
  font-size: 11px;
}
.st-text.big {
  font-size: 18px;
  font-weight: 800;
}
.st-text.title {
  font-size: 13px;
  font-weight: 800;
  fill: var(--muted);
  letter-spacing: 0.06em;
  text-transform: uppercase;
}
.st-text.mono {
  font-family: "JetBrains Mono", monospace;
}
.st-text.ok {
  fill: var(--ok);
}
.st-text.bad {
  fill: var(--bad);
}
.st-text.accent {
  fill: var(--accent-2);
}
.st-line {
  stroke: color-mix(in srgb, var(--muted) 55%, transparent);
  stroke-width: 2;
  fill: none;
}
.st-ring {
  stroke: color-mix(in srgb, var(--muted) 50%, transparent);
  stroke-width: 3;
  fill: none;
}
.sbox rect {
  fill: var(--panel);
  stroke: var(--border);
  stroke-width: 1.5;
  transition: fill 0.3s, stroke 0.3s;
}
.sbox-text {
  fill: var(--text);
  font-size: 12px;
  font-weight: 600;
}
.sbox.mono .sbox-text {
  font-family: "JetBrains Mono", monospace;
}
.sbox.on rect {
  fill: color-mix(in srgb, var(--accent-2) 30%, var(--panel));
  stroke: var(--accent-2);
}
.sbox.ok rect {
  fill: color-mix(in srgb, var(--ok) 28%, var(--panel));
  stroke: var(--ok);
}
.sbox.bad rect {
  fill: color-mix(in srgb, var(--bad) 28%, var(--panel));
  stroke: var(--bad);
}
.sbox.warn rect {
  fill: color-mix(in srgb, var(--warn) 28%, var(--panel));
  stroke: var(--warn);
}
.sbox.purple rect {
  fill: color-mix(in srgb, var(--accent) 30%, var(--panel));
  stroke: var(--accent);
}
.sbox.dim {
  opacity: 0.35;
}
.sbox.ghost rect {
  fill: transparent;
  stroke-dasharray: 4 4;
}

/* ------------------------------------------------------------ playground */
.pg-task {
  padding: 12px 14px;
  margin-bottom: 12px;
  border-radius: 12px;
  background: color-mix(in srgb, var(--accent) 10%, var(--panel));
  border: 1px solid color-mix(in srgb, var(--accent) 35%, var(--border));
  font-size: 15px;
}
.pg-task > :first-child {
  margin-top: 0;
}
.pg-task > :last-child {
  margin-bottom: 0;
}
.pg-task code {
  font-size: 0.88em;
  padding: 1px 5px;
  border-radius: 5px;
  background: var(--code-bg);
}
.pg-editor {
  max-height: 520px;
  overflow: auto;
  border-radius: 12px;
  border: 1px solid var(--border);
  background: var(--code-bg);
}
.pg-inner {
  display: grid;
  grid-template-columns: auto 1fr;
  min-width: max-content;
}
.pg-gutter {
  padding: 14px 10px 14px 14px;
  text-align: right;
  color: var(--tok-c);
  user-select: none;
  white-space: pre;
  border-right: 1px solid var(--border);
}
.pg-code {
  display: grid;
}
.pg-gutter,
.pg-hl,
.pg-code textarea {
  font: 13.5px/1.6 "JetBrains Mono", ui-monospace, Consolas, monospace;
  font-variant-ligatures: none;
  tab-size: 2;
}
.pg-hl,
.pg-code textarea {
  grid-area: 1 / 1;
  margin: 0;
  padding: 14px 16px;
  white-space: pre;
  overflow: hidden;
  border: 0;
}
.pg-hl {
  pointer-events: none;
  color: var(--text);
}
.pg-code textarea {
  resize: none;
  background: transparent;
  color: transparent;
  caret-color: var(--accent-2);
  outline: none;
  min-height: 120px;
}
.pg-code textarea::selection {
  background: color-mix(in srgb, var(--accent) 35%, transparent);
  color: transparent;
}
.tok-k { color: var(--tok-k); }
.tok-s { color: var(--tok-s); }
.tok-n { color: var(--tok-n); }
.tok-c { color: var(--tok-c); font-style: italic; }
.tok-f { color: var(--tok-f); }
.pg-bar {
  display: flex;
  gap: 8px;
  align-items: center;
  flex-wrap: wrap;
  margin: 10px 0;
}
.pg-status {
  font-size: 13px;
  font-weight: 600;
  color: var(--muted);
}
.pg-status.ok {
  color: var(--ok);
}
.pg-status.err {
  color: var(--bad);
}
.pg-status.warn {
  color: var(--warn);
}
.pg-hint {
  padding: 10px 14px;
  border-radius: 10px;
  margin-bottom: 10px;
  background: color-mix(in srgb, var(--warn) 10%, var(--panel));
  border: 1px solid color-mix(in srgb, var(--warn) 35%, var(--border));
  font-size: 14.5px;
}
.pg-out {
  min-height: 70px;
  max-height: 320px;
  overflow: auto;
  border-radius: 12px;
  padding: 12px 14px;
  background: #060914;
  color: #d8def5;
  border: 1px solid var(--border);
  font: 13px/1.6 "JetBrains Mono", monospace;
  white-space: pre-wrap;
  word-break: break-word;
}
.pg-out-empty {
  color: #6b7599;
  font-family: Inter, sans-serif;
}
.out-warn {
  color: #fbbf24;
}
.out-error {
  color: #f87171;
}

/* ------------------------------------------------------------ quiz */
.q {
  padding: 14px 0;
  border-bottom: 1px solid var(--border);
}
.q:last-child {
  border-bottom: none;
}
.q-text {
  margin: 0 0 10px;
  font-weight: 600;
}
.q-opts {
  display: grid;
  gap: 8px;
}
.q-opt {
  text-align: left;
  padding: 10px 14px;
  border-radius: 12px;
  border: 1px solid var(--border);
  background: var(--panel-2);
  color: var(--text);
  font: 15px Inter, sans-serif;
  cursor: pointer;
  transition: border-color 0.15s, background 0.15s;
}
.q-opt:hover {
  border-color: var(--border-strong);
  background: color-mix(in srgb, var(--text) 4%, var(--panel-2));
}
.q.answered .q-opt {
  cursor: default;
}
.q.answered .q-opt:not(.right):not(.wrong) {
  opacity: 0.6;
}
.q-opt.right {
  border-color: var(--ok);
  background: color-mix(in srgb, var(--ok) 16%, var(--panel-2));
}
.q-opt.wrong {
  border-color: var(--bad);
  background: color-mix(in srgb, var(--bad) 16%, var(--panel-2));
  animation: shake 0.35s;
}
@keyframes shake {
  25% { transform: translateX(-5px); }
  75% { transform: translateX(5px); }
}
.q-why {
  margin-top: 10px;
  font-size: 14.5px;
  color: var(--muted);
  animation: fadeUp 0.3s;
}
.result {
  display: flex;
  align-items: center;
  gap: 12px;
  flex-wrap: wrap;
  padding: 14px 16px;
  border-radius: 12px;
  margin-top: 12px;
}
.result.pass {
  background: color-mix(in srgb, var(--ok) 14%, transparent);
  border: 1px solid var(--ok);
}
.result.fail {
  background: color-mix(in srgb, var(--warn) 12%, transparent);
  border: 1px solid var(--warn);
}

.ch-nav {
  display: flex;
  justify-content: space-between;
  gap: 12px;
  flex-wrap: wrap;
  margin-top: 30px;
}

/* ------------------------------------------------------------ toast / confetti */
.toast {
  position: fixed;
  left: 50%;
  bottom: 28px;
  transform: translateX(-50%);
  z-index: 100;
  padding: 12px 20px;
  border-radius: 14px;
  background: var(--panel);
  border: 1px solid var(--border);
  box-shadow: var(--shadow-lg);
  font-weight: 600;
  animation: toastIn 0.35s ease;
  transition: opacity 0.5s, transform 0.5s;
}
.toast.out {
  opacity: 0;
  transform: translate(-50%, 10px);
}
@keyframes toastIn {
  from {
    opacity: 0;
    transform: translate(-50%, 16px);
  }
}
.confetti {
  position: fixed;
  top: -12px;
  z-index: 99;
  width: 9px;
  height: 14px;
  border-radius: 2px;
  pointer-events: none;
  animation: fall linear forwards;
}
@keyframes fall {
  to {
    top: 105vh;
    transform: rotate(720deg) translateX(40px);
  }
}

/* ------------------------------------------------------------ responsive */
.scrim {
  display: none;
}
@media (max-width: 960px) {
  .layout {
    grid-template-columns: minmax(0, 1fr);
  }
  .menu-btn {
    display: inline-flex;
  }
  .sidebar {
    position: fixed;
    top: 60px;
    left: 0;
    bottom: 0;
    width: 290px;
    max-width: 85vw;
    z-index: 40;
    background: var(--bg);
    transform: translateX(-100%);
    transition: transform 0.25s;
  }
  body.nav-open .sidebar {
    transform: none;
  }
  body.nav-open .scrim {
    display: block;
    position: fixed;
    inset: 60px 0 0;
    background: rgba(0, 0, 0, 0.45);
    z-index: 35;
  }
  .hero {
    grid-template-columns: 1fr;
  }
  .how {
    grid-template-columns: 1fr 1fr;
  }
}
@media (max-width: 600px) {
  .page {
    padding: 20px 16px 60px;
  }
  .card {
    padding: 16px;
    border-radius: 14px;
  }
  .tab-panel {
    padding: 10px;
  }
  .how {
    grid-template-columns: 1fr;
  }
  .compare {
    grid-template-columns: 1fr;
  }
  .topbar {
    gap: 8px;
    padding: 0 12px;
  }
  .xp-bar {
    display: none;
  }
  .brand {
    min-width: 0;
  }
  .brand span:last-child {
    font-size: 14px;
    overflow: hidden;
    text-overflow: ellipsis;
  }
  .sec-head h2 {
    font-size: 20px;
  }
}
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
  }
}

/* bars used by dashboard-style scenes */
.bar-bg {
  fill: var(--panel);
  stroke: var(--border);
}
.bar {
  fill: var(--accent-2);
  transition: fill 0.3s;
}
.bar.hot {
  fill: var(--bad);
}
.bar.ok {
  fill: var(--ok);
}
.bar.warn {
  fill: var(--warn);
}
.bar.purple {
  fill: var(--accent);
}

/* chat bubbles used by dialog-style scenes */
.bubble rect {
  fill: var(--panel);
  stroke: var(--border);
  stroke-width: 1.5;
}
.bubble text {
  fill: var(--text);
  font-size: 12.5px;
}
.bubble.left rect {
  fill: color-mix(in srgb, var(--k-client) 16%, var(--panel));
  stroke: var(--k-client);
}
.bubble.right rect {
  fill: color-mix(in srgb, var(--accent) 16%, var(--panel));
  stroke: var(--accent);
}
.bubble.sys rect {
  fill: color-mix(in srgb, var(--ok) 14%, var(--panel));
  stroke: var(--ok);
}
.ring-arc,
.ring-arc[class*="c"] {
  fill: none !important;
  stroke-width: 10;
  stroke-linecap: round;
  opacity: 0.55;
  transition: opacity 0.3s;
}
.ring-dot {
  stroke: var(--panel);
  stroke-width: 2;
}
.c0 { stroke: #60a5fa; fill: #60a5fa; }
.c1 { stroke: #34d399; fill: #34d399; }
.c2 { stroke: #f472b6; fill: #f472b6; }
.c3 { stroke: #fbbf24; fill: #fbbf24; }
.c4 { stroke: #a78bfa; fill: #a78bfa; }
.c5 { stroke: #fb923c; fill: #fb923c; }
.c6 { stroke: #2dd4bf; fill: #2dd4bf; }
.c7 { stroke: #f87171; fill: #f87171; }
.tl-axis {
  stroke: var(--muted);
  stroke-width: 1.5;
}
.tl-win {
  fill: color-mix(in srgb, var(--accent-2) 10%, transparent);
  stroke: var(--accent-2);
  stroke-width: 1.5;
  stroke-dasharray: 5 4;
}
.tl-win.bad {
  fill: color-mix(in srgb, var(--bad) 12%, transparent);
  stroke: var(--bad);
}
.dot-ok { fill: var(--ok); }
.dot-bad { fill: var(--bad); }
.dot-info { fill: var(--accent-2); }
.dot-warn { fill: var(--warn); }

/* ------------------------------------------------------------ map scenes (proximity service) */
.geo-map {
  fill: color-mix(in srgb, var(--k-cdn) 5%, var(--panel));
  stroke: var(--border-strong);
  stroke-width: 1.2;
}
.geo-pt {
  fill: var(--muted);
  transition: fill 0.3s, opacity 0.3s;
}
.geo-pt.hit,
.geo-pt.both {
  fill: var(--ok);
}
.geo-pt.lat {
  fill: var(--warn);
}
.geo-pt.lng {
  fill: var(--k-lb);
}
.geo-pt.dim {
  opacity: 0.25;
}
.geo-user {
  fill: var(--k-client);
  stroke: var(--panel);
  stroke-width: 2.5;
}
.geo-radius {
  fill: color-mix(in srgb, var(--k-client) 12%, transparent);
  stroke: var(--k-client);
  stroke-width: 1.6;
  stroke-dasharray: 5 4;
}
.geo-band.lat {
  fill: color-mix(in srgb, var(--warn) 14%, transparent);
}
.geo-band.lng {
  fill: color-mix(in srgb, var(--k-lb) 16%, transparent);
}
.geo-split {
  stroke: var(--accent);
  stroke-width: 1.4;
  stroke-dasharray: 4 3;
}
.geo-cell {
  fill: color-mix(in srgb, var(--accent) 18%, transparent);
  stroke: var(--accent);
  stroke-width: 1.4;
}
.geo-neigh {
  fill: color-mix(in srgb, var(--ok) 12%, transparent);
  stroke: color-mix(in srgb, var(--ok) 60%, transparent);
  stroke-width: 1;
}

/* ------------------------------------------------------------ custom drop-downs (js/select.js) */
.ui-select-native {
  position: absolute !important;
  width: 1px !important;
  height: 1px !important;
  padding: 0 !important;
  border: 0 !important;
  opacity: 0 !important;
  pointer-events: none !important;
  overflow: hidden;
}
.ui-select {
  display: inline-flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
  width: 100%;
  min-width: 0;
  padding: 9px 12px;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--bg-2);
  color: var(--text);
  font: 500 14.5px/1.4 Inter, system-ui, sans-serif;
  text-align: left;
  cursor: pointer;
  transition: border-color 0.15s, background 0.15s, box-shadow 0.15s;
}
.ui-select:hover:not(:disabled) {
  border-color: var(--border-strong);
}
.ui-select:focus-visible,
.ui-select.open {
  outline: none;
  border-color: var(--accent);
  box-shadow: var(--focus);
}
.ui-select:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}
.ui-select.placeholder .ui-select-value {
  color: var(--muted);
}
.ui-select-value {
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}
.ui-select-chev {
  flex: none;
  color: var(--muted);
  transition: transform 0.2s;
}
.ui-select.open .ui-select-chev {
  transform: rotate(180deg);
}
.ui-select-pop {
  position: fixed;
  z-index: 1000;
  display: flex;
  flex-direction: column;
  border: 1px solid var(--border-strong);
  border-radius: 12px;
  background: var(--panel);
  box-shadow: var(--shadow-lg), 0 0 0 1px rgba(0, 0, 0, 0.04);
  overflow: hidden;
  animation: ui-select-in 0.12s ease-out;
}
.ui-select-pop.up {
  animation-name: ui-select-up;
}
@keyframes ui-select-in {
  from {
    opacity: 0;
    transform: translateY(-4px);
  }
}
@keyframes ui-select-up {
  from {
    opacity: 0;
    transform: translateY(4px);
  }
}
.ui-select-search {
  padding: 8px 8px 4px;
  border-bottom: 1px solid var(--border);
}
.ui-select-search input {
  width: 100%;
  padding: 7px 10px;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--bg-2);
  color: var(--text);
  font: 14px Inter, system-ui, sans-serif;
}
.ui-select-search input:focus {
  outline: none;
  border-color: var(--accent);
}
.ui-select-list {
  list-style: none;
  margin: 0;
  padding: 6px;
  overflow-y: auto;
  overscroll-behavior: contain;
}
.ui-select-opt {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
  padding: 8px 10px;
  border-radius: 8px;
  font-size: 14px;
  color: var(--text);
  cursor: pointer;
}
.ui-select-opt.active {
  background: var(--panel-2);
}
.ui-select-opt[aria-selected="true"] {
  color: var(--accent);
  font-weight: 600;
}
.ui-select-opt[aria-selected="true"] svg {
  flex: none;
}
.ui-select-opt[aria-disabled="true"] {
  opacity: 0.45;
  cursor: default;
}
.ui-select-group {
  padding: 8px 10px 4px;
  font-size: 11.5px;
  font-weight: 700;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--muted);
}
.ui-select-empty {
  padding: 10px;
  font-size: 13.5px;
  color: var(--muted);
}

/* compact drop-downs that sit inline in toolbars */
.speed .ui-select,
.coach-head .ui-select,
.bank-toolbar .ui-select,
.flash-filter .ui-select {
  width: auto;
  padding: 7px 10px;
  font-size: 13.5px;
  background: var(--panel);
}
.speed .ui-select {
  padding: 4px 8px;
  font-size: 13px;
  gap: 6px;
}
.coach-head .ui-select {
  padding: 4px 8px;
  font-size: 13px;
}
.flash-filter .ui-select {
  min-width: 260px;
}
.ed-props .ui-select {
  padding: 7px 10px;
  font-size: 13.5px;
}