:root {
  --bg: #ffffff;
  --bg-soft: #f7f7f8;
  --surface: #ffffff;
  --text: #111318;
  --text-2: #4b5563;
  --text-3: #5f6673;
  --border: #e3e5e8;
  --border-strong: #cfd3d8;
  --accent: #b83a1f;
  --accent-hover: #9e2f18;
  --accent-soft: #fdf0ec;
  --success: #1f7a4d;
  --error: #b42318;
  --info: #1f6f8b;
  --code-bg: #ffffff;
  --code-fg: #010409;
  --code-comment: #4b535d;
  --term-bg: #0a0c10;
  --term-fg: #f0f3f6;
  --mono: "SFMono-Regular", Menlo, Consolas, "Liberation Mono", monospace;
  --sans: "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Avenir Next",
    "Helvetica Neue", sans-serif;
  --display: "Avenir Next", "PingFang SC", "Hiragino Sans GB", sans-serif;
  --shadow: 0 1px 2px rgba(17, 19, 24, 0.04),
    0 8px 24px rgba(17, 19, 24, 0.05);
  --nav-h: 56px;
  --rail-w: 252px;
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--nav-h) + 18px);
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--sans);
  font-size: 16.5px;
  line-height: 1.72;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }
  *,
  *::before,
  *::after {
    animation-duration: 0.001ms !important;
    transition-duration: 0.001ms !important;
  }
}

/* ---------- top nav ---------- */
.topnav {
  position: fixed;
  inset: 0 0 auto 0;
  height: var(--nav-h);
  background: rgba(255, 255, 255, 0.92);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--border);
  z-index: 50;
  display: flex;
  align-items: center;
  gap: 18px;
  padding: 0 22px;
}

.brand {
  font-family: var(--display);
  font-weight: 700;
  letter-spacing: -0.01em;
  font-size: 15px;
  white-space: nowrap;
}

.brand .brand-mark {
  display: inline-block;
  width: 9px;
  height: 9px;
  background: var(--accent);
  margin-right: 8px;
  transform: rotate(45deg);
}

.navmeta {
  font-family: var(--mono);
  font-size: 11.5px;
  color: var(--text-3);
  letter-spacing: 0.02em;
  white-space: nowrap;
}

.navlinks {
  margin-left: auto;
  display: flex;
  gap: 6px;
}

.navlinks a {
  font-size: 13px;
  color: var(--text-2);
  text-decoration: none;
  padding: 6px 9px;
  border-radius: 6px;
}

.navlinks a:hover {
  background: var(--bg-soft);
  color: var(--text);
}

.progress-track {
  position: fixed;
  top: var(--nav-h);
  left: 0;
  right: 0;
  height: 2px;
  background: transparent;
  z-index: 51;
}

.progress-bar {
  height: 2px;
  width: 0;
  background: var(--accent);
}

/* ---------- shell ---------- */
.shell {
  display: grid;
  grid-template-columns: var(--rail-w) minmax(0, 1fr);
  align-items: start;
  padding-top: var(--nav-h);
}

.rail {
  position: sticky;
  top: calc(var(--nav-h) + 2px);
  height: calc(100vh - var(--nav-h) - 2px);
  overflow-y: auto;
  border-right: 1px solid var(--border);
  padding: 28px 18px 40px 24px;
}

.rail-kicker {
  font-family: var(--mono);
  font-size: 10.5px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--text-3);
  margin: 0 0 14px;
}

.rail-list {
  list-style: none;
  margin: 0;
  padding: 0;
}

.rail-module {
  font-family: var(--mono);
  font-size: 10.5px;
  letter-spacing: 0.06em;
  color: var(--text-3);
  margin: 18px 0 6px;
}

.rail-list li a {
  display: grid;
  grid-template-columns: 10px 1fr;
  gap: 9px;
  align-items: baseline;
  text-decoration: none;
  color: var(--text-2);
  font-size: 13.2px;
  line-height: 1.45;
  padding: 5px 0;
}

.rail-list li a .dot {
  width: 7px;
  height: 7px;
  border: 1px solid var(--border-strong);
  border-radius: 50%;
  transform: translateY(-1px);
}

.rail-list li a.active {
  color: var(--text);
  font-weight: 600;
}

.rail-list li a.active .dot {
  background: var(--accent);
  border-color: var(--accent);
}

.rail-list li a .rt {
  display: block;
  font-family: var(--mono);
  font-size: 10.5px;
  color: var(--text-3);
  font-weight: 400;
}

.rail-foot {
  margin-top: 26px;
  padding-top: 16px;
  border-top: 1px solid var(--border);
  font-size: 11.5px;
  color: var(--text-3);
  line-height: 1.6;
}

.rail-next {
  font-family: var(--mono);
  font-size: 11px;
  color: var(--accent);
}

/* ---------- main ---------- */
main {
  min-width: 0;
}

.wrap {
  max-width: 860px;
  margin: 0 auto;
  padding: 0 32px;
}

.wide {
  max-width: 1060px;
}

.hero {
  padding: 66px 0 26px;
  border-bottom: 1px solid var(--border);
}

.eyebrow {
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--accent);
  margin: 0 0 16px;
}

h1 {
  font-family: var(--display);
  font-size: clamp(38px, 5.6vw, 62px);
  line-height: 1.04;
  letter-spacing: -0.035em;
  margin: 0 0 18px;
  font-weight: 800;
}

.hero .lede {
  font-size: 19px;
  color: var(--text-2);
  max-width: 70ch;
  margin: 0 0 22px;
}

.meta-row {
  display: flex;
  flex-wrap: wrap;
  gap: 8px 20px;
  font-family: var(--mono);
  font-size: 11.5px;
  color: var(--text-3);
  letter-spacing: 0.02em;
  margin-bottom: 26px;
}

.meta-row strong {
  color: var(--text);
  font-weight: 600;
}

.hero-grid {
  display: grid;
  grid-template-columns: 1.15fr 0.85fr;
  gap: 26px;
  align-items: start;
}

.start-card {
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 20px 22px;
  background: var(--surface);
  box-shadow: var(--shadow);
}

.start-card h2 {
  font-size: 17px;
  margin: 0 0 8px;
}

.start-card p {
  font-size: 14px;
  color: var(--text-2);
  margin: 0 0 14px;
}

.start-card ol {
  margin: 0;
  padding-left: 18px;
  font-size: 14px;
  color: var(--text-2);
}

.start-card li {
  margin-bottom: 6px;
}

.video-block {
  margin: 30px 0 10px;
}

.video-block video {
  width: 100%;
  aspect-ratio: 16 / 9;
  display: block;
  background: #0a0c10;
  border-radius: 10px;
  border: 1px solid var(--border);
}

.video-block figcaption {
  font-size: 12.5px;
  color: var(--text-3);
  margin-top: 8px;
  display: flex;
  justify-content: space-between;
  gap: 16px;
}

.pages-note {
  background: var(--accent-soft);
  border-bottom: 1px solid #f2d4cb;
  padding: 10px 0;
  font-size: 13px;
  color: var(--text-2);
}

.pages-note code {
  font-family: var(--mono);
  font-size: 11.5px;
  background: #fff;
  border: 1px solid #f2d4cb;
  border-radius: 4px;
  padding: 1px 5px;
}

/* ---------- modules / sections ---------- */
.module {
  padding: 54px 0 12px;
  border-top: 1px solid var(--border);
  margin-top: 40px;
}

.module:first-of-type {
  border-top: 0;
  margin-top: 0;
}

.module-head {
  margin-bottom: 30px;
}

.module-num {
  font-family: var(--display);
  font-size: 64px;
  font-weight: 800;
  line-height: 0.8;
  color: var(--accent);
  opacity: 0.18;
  letter-spacing: -0.04em;
  margin: 0 0 6px;
}

.module h2 {
  font-family: var(--display);
  font-size: clamp(26px, 3.4vw, 36px);
  letter-spacing: -0.025em;
  line-height: 1.15;
  margin: 0 0 10px;
}

.module .lede {
  color: var(--text-2);
  max-width: 68ch;
  margin: 0;
  font-size: 16.5px;
}

.section {
  padding: 18px 0 40px;
  border-top: 1px dashed var(--border);
}

.section:first-of-type {
  border-top: 0;
}

.section h3 {
  font-family: var(--display);
  font-size: 23px;
  letter-spacing: -0.015em;
  line-height: 1.3;
  margin: 14px 0 6px;
}

.section-label {
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--text-3);
}

.timechip {
  display: inline-block;
  font-family: var(--mono);
  font-size: 11px;
  color: var(--text-3);
  background: var(--bg-soft);
  border-radius: 4px;
  padding: 2px 8px;
  margin-left: 8px;
  vertical-align: 2px;
}

.screen {
  margin: 20px 0 22px;
}

h4 {
  font-family: var(--display);
  font-size: 17.5px;
  letter-spacing: -0.01em;
  margin: 26px 0 8px;
}

p {
  margin: 0 0 14px;
}

.prose p,
.prose ul,
.prose ol {
  max-width: 72ch;
}

ul,
ol {
  padding-left: 22px;
  margin: 0 0 16px;
}

li {
  margin-bottom: 6px;
}

strong {
  font-weight: 650;
}

a {
  color: var(--accent);
  text-underline-offset: 3px;
}

abbr.term {
  text-decoration: none;
  border-bottom: 1px dotted var(--text-3);
  cursor: help;
  position: relative;
}

.tooltip {
  position: fixed;
  z-index: 90;
  max-width: 300px;
  background: #111318;
  color: #fff;
  font-size: 12.5px;
  line-height: 1.55;
  padding: 8px 10px;
  border-radius: 6px;
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.18);
  pointer-events: none;
  opacity: 0;
  transform: translateY(4px);
  transition: opacity 0.12s ease, transform 0.12s ease;
}

.tooltip.show {
  opacity: 1;
  transform: translateY(0);
}

/* ---------- diagrams ---------- */
figure.diagram {
  margin: 22px 0;
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 18px 18px 12px;
  background: var(--surface);
}

figure.diagram .mermaid-wrap {
  overflow-x: auto;
  text-align: center;
}

figure.diagram svg {
  max-width: 100%;
  height: auto;
}

figure.diagram figcaption {
  font-size: 12.8px;
  color: var(--text-3);
  border-top: 1px solid var(--border);
  padding-top: 9px;
  margin-top: 8px;
}

figure.diagram details {
  margin-top: 6px;
  font-size: 12px;
  color: var(--text-3);
}

figure.diagram summary {
  cursor: pointer;
  font-family: var(--mono);
  font-size: 10.5px;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.diagram-note {
  font-family: var(--mono);
  font-size: 10.5px;
  color: var(--accent);
  letter-spacing: 0.06em;
  text-transform: uppercase;
  margin-bottom: 8px;
}

/* ---------- code ---------- */
.code {
  margin: 18px 0;
  border: 1px solid var(--border);
  border-radius: 8px;
  overflow: hidden;
  background: var(--code-bg);
}

.code .code-head {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
  padding: 7px 12px;
  border-bottom: 1px solid var(--border);
  background: var(--bg-soft);
  font-family: var(--mono);
  font-size: 11px;
  color: var(--text-3);
}

.code pre {
  margin: 0;
  padding: 14px 16px;
  overflow-x: auto;
  font-family: var(--mono);
  font-size: 12.8px;
  line-height: 1.62;
  color: var(--code-fg);
  tab-size: 4;
}

.code pre code {
  font-family: inherit;
}

.code .ln {
  color: #4B5563;
  user-select: none;
  display: inline-block;
  width: 2.4em;
  text-align: right;
  margin-right: 1em;
}

.code .cm {
  color: var(--code-comment);
}

.code .kw {
  color: #a0111f;
}

.code .st {
  color: #024c1a;
}

.code .fn {
  color: #622cbc;
}

.code .nu {
  color: #0349b4;
}

pre.term {
  background: var(--term-bg);
  color: var(--term-fg);
  border: 0;
  border-radius: 8px;
  padding: 13px 16px;
  font-family: var(--mono);
  font-size: 12.8px;
  line-height: 1.65;
  white-space: pre-wrap;
  overflow-wrap: anywhere;
  margin: 16px 0;
}

pre.term .p {
  color: #A9B1BA;
  user-select: none;
}

pre.term .o {
  color: #ffd8a8;
}

.copy {
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text-2);
  font-family: var(--mono);
  font-size: 10.5px;
  padding: 3px 8px;
  border-radius: 4px;
  cursor: pointer;
}

.copy:hover {
  border-color: var(--border-strong);
  color: var(--text);
}

/* translation */
.translate {
  display: grid;
  grid-template-columns: 1.05fr 0.95fr;
  gap: 0;
  border: 1px solid var(--border);
  border-left: 3px solid var(--accent);
  border-radius: 8px;
  margin: 18px 0;
  overflow: hidden;
}

.translate .t-code,
.translate .t-en {
  padding: 14px 16px;
  font-size: 12.8px;
  line-height: 1.75;
}

.translate .t-code {
  font-family: var(--mono);
  background: var(--surface);
  border-right: 1px solid var(--border);
  white-space: pre-wrap;
  overflow-wrap: anywhere;
}

.translate .t-en {
  background: var(--bg-soft);
  color: var(--text-2);
}

.translate .t-en p {
  margin: 0 0 9px;
}

.translate .t-en p:last-child {
  margin-bottom: 0;
}

.translate .t-en b {
  color: var(--text);
}

/* callout */
.callout {
  border-left: 3px solid var(--accent);
  background: var(--accent-soft);
  padding: 12px 16px;
  border-radius: 0 6px 6px 0;
  margin: 18px 0;
  font-size: 15px;
}

.callout p:last-child {
  margin-bottom: 0;
}

.callout .label {
  font-family: var(--mono);
  font-size: 10.5px;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--accent);
  display: block;
  margin-bottom: 4px;
}

/* ---------- micro checks ---------- */
.micro {
  border-top: 1px solid var(--border);
  border-bottom: 1px solid var(--border);
  padding: 16px 0;
  margin: 26px 0;
}

.micro-q {
  font-size: 14.5px;
  font-weight: 600;
  margin: 0 0 10px;
}

.micro-q .tag {
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--accent);
  margin-right: 8px;
}

.micro-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.micro button,
.order button {
  border: 1px solid var(--border-strong);
  background: var(--surface);
  color: var(--text);
  font-family: var(--sans);
  font-size: 13.5px;
  padding: 6px 12px;
  border-radius: 6px;
  cursor: pointer;
}

.micro button:hover,
.order button:hover {
  border-color: var(--accent);
}

.micro button.picked,
.order button.picked {
  border-color: var(--accent);
  background: var(--accent-soft);
}

.micro button.good {
  border-color: var(--success);
  color: var(--success);
}

.micro button.bad {
  border-color: var(--error);
  color: var(--error);
}

.micro-result {
  margin-top: 10px;
  font-size: 14px;
  color: var(--text-2);
  padding-left: 12px;
  border-left: 2px solid var(--success);
}

.order-pool,
.order-seq {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  align-items: center;
  min-height: 38px;
  margin-bottom: 10px;
}

.order-seq {
  border: 1px dashed var(--border-strong);
  border-radius: 6px;
  padding: 8px;
  min-height: 46px;
}

.order-seq:empty::before {
  content: "按顺序点击下面的步骤";
  font-size: 12px;
  color: var(--text-3);
}

.order-status {
  font-size: 13px;
  color: var(--text-2);
  min-height: 1.4em;
}

/* ---------- 60-second hands-on ---------- */
.tryit {
  border: 1px solid var(--border);
  border-left: 3px solid var(--accent);
  border-radius: 0 8px 8px 0;
  padding: 15px 18px;
  margin: 26px 0;
  background: var(--surface);
}

.tryit-head {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  gap: 12px;
  margin-bottom: 4px;
}

.tryit-head .label {
  font-family: var(--mono);
  font-size: 10.5px;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--accent);
}

.tryit-head .t {
  font-family: var(--mono);
  font-size: 10.5px;
  color: var(--text-3);
}

.tryit p {
  font-size: 14.5px;
  color: var(--text-2);
  margin: 0 0 10px;
}

.tryit p.tryit-note {
  margin: 10px 0 0;
  font-size: 13.5px;
}

.tryit pre.term {
  margin: 8px 0;
  font-size: 12.5px;
}

.tryit details {
  margin: 4px 0 0;
}

.tryit details summary {
  cursor: pointer;
  font-family: var(--mono);
  font-size: 10.5px;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--accent);
  padding: 4px 0;
}

/* ---------- gate: MC ---------- */
.gate {
  margin: 34px 0 8px;
}

.gate-step {
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--surface);
  padding: 18px 20px;
  margin-bottom: 14px;
}

.gate-step-head {
  display: flex;
  align-items: baseline;
  gap: 10px;
  margin-bottom: 14px;
}

.step-num {
  width: 22px;
  height: 22px;
  border-radius: 50%;
  background: var(--accent);
  color: #fff;
  font-family: var(--mono);
  font-size: 11px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  flex: none;
  transform: translateY(2px);
}

.gate-step h4 {
  margin: 0;
  font-size: 15.5px;
}

.gate-time {
  font-family: var(--mono);
  font-size: 10.5px;
  color: var(--text-3);
  margin-left: auto;
}

fieldset.mc {
  border: 0;
  padding: 0;
  margin: 0 0 18px;
}

fieldset.mc:last-child {
  margin-bottom: 0;
}

fieldset.mc legend {
  font-size: 14.5px;
  font-weight: 600;
  padding: 0;
  margin-bottom: 8px;
  line-height: 1.55;
}

fieldset.mc legend .qnum {
  font-family: var(--mono);
  color: var(--text-3);
  margin-right: 6px;
}

label.opt {
  display: grid;
  grid-template-columns: 22px 1fr;
  gap: 8px;
  align-items: start;
  padding: 7px 10px;
  border: 1px solid transparent;
  border-radius: 6px;
  cursor: pointer;
  font-size: 14.5px;
  line-height: 1.55;
}

label.opt:hover {
  background: var(--bg-soft);
}

label.opt input {
  margin: 4px 0 0;
  accent-color: var(--accent);
}

label.opt .opt-key {
  font-family: var(--mono);
  font-size: 11px;
  color: var(--text-3);
}

label.opt .opt-why {
  display: none;
  grid-column: 2;
  font-size: 12.8px;
  color: var(--text-2);
  margin-top: 3px;
}

label.opt.answered .opt-why {
  display: block;
}

label.opt.correct {
  border-color: #9fd3b9;
  background: #f2fbf6;
}

label.opt.wrong {
  border-color: #f0b4ae;
  background: #fdf4f3;
}

label.opt .mark {
  font-family: var(--mono);
  font-size: 11px;
  margin-left: 6px;
}

label.opt.correct .mark {
  color: var(--success);
}

label.opt.wrong .mark {
  color: var(--error);
}

.mc-foot {
  display: flex;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
  margin-top: 8px;
}

.btn {
  border: 1px solid var(--accent);
  background: var(--accent);
  color: #fff;
  font-family: var(--sans);
  font-size: 13.5px;
  font-weight: 600;
  padding: 7px 15px;
  border-radius: 6px;
  cursor: pointer;
}

.btn:hover {
  background: var(--accent-hover);
}

.btn.secondary {
  background: var(--surface);
  color: var(--text);
  border-color: var(--border-strong);
  font-weight: 500;
}

.btn.secondary:hover {
  border-color: var(--accent);
  color: var(--accent);
}

.btn.small {
  font-size: 12px;
  padding: 5px 10px;
}

.textbtn {
  border: 0;
  background: none;
  color: var(--accent);
  font-family: var(--sans);
  font-size: 12.5px;
  padding: 4px 2px;
  cursor: pointer;
  text-decoration: underline;
  text-underline-offset: 3px;
}

.mc-result {
  font-size: 13.5px;
  margin-top: 8px;
}

.mc-result.good {
  color: var(--success);
}

.mc-result.bad {
  color: var(--error);
}

.mc-why {
  font-size: 13.5px;
  color: var(--text-2);
  background: var(--bg-soft);
  border-radius: 6px;
  padding: 8px 10px;
  margin-top: 8px;
}

/* ---------- short answer ---------- */
.sa {
  margin-top: 2px;
}

.sa label.sa-label {
  display: block;
  font-size: 14.5px;
  font-weight: 600;
  margin-bottom: 8px;
  line-height: 1.55;
}

.sa textarea {
  width: 100%;
  min-height: 110px;
  resize: vertical;
  border: 1px solid var(--border-strong);
  border-radius: 8px;
  padding: 10px 12px;
  font-family: var(--sans);
  font-size: 14.5px;
  line-height: 1.65;
  color: var(--text);
  background: var(--surface);
}

.sa textarea:focus {
  outline: 2px solid var(--accent);
  outline-offset: 1px;
  border-color: var(--accent);
}

.sa-meta {
  display: flex;
  gap: 14px;
  align-items: center;
  font-family: var(--mono);
  font-size: 11px;
  color: var(--text-3);
  margin: 6px 0 10px;
}

.sa-meta .spacer {
  margin-left: auto;
}

.sa-actions {
  display: flex;
  gap: 12px;
  align-items: center;
  flex-wrap: wrap;
}

.model {
  margin-top: 14px;
  border-left: 3px solid var(--accent);
  background: var(--accent-soft);
  border-radius: 0 8px 8px 0;
  padding: 13px 16px;
  font-size: 14.3px;
  color: var(--text);
}

.model p {
  margin: 0 0 10px;
}

.model .model-kicker {
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--accent);
  display: block;
  margin-bottom: 5px;
}

.selfcheck {
  margin-top: 12px;
  display: grid;
  gap: 7px;
}

.selfcheck label {
  font-size: 13px;
  color: var(--text-2);
  display: flex;
  gap: 8px;
  align-items: flex-start;
  cursor: pointer;
}

.selfcheck input {
  margin-top: 3px;
  accent-color: var(--accent);
}

/* ---------- lab ---------- */
.lab {
  border: 1px solid var(--border-strong);
  border-radius: 12px;
  background: var(--surface);
  box-shadow: var(--shadow);
  margin: 30px 0 40px;
  overflow: hidden;
}

.lab-head {
  padding: 18px 22px;
  border-bottom: 1px solid var(--border);
  background: var(--bg-soft);
}

.lab-head .lab-kicker {
  font-family: var(--mono);
  font-size: 10.5px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--accent);
  margin-bottom: 4px;
}

.lab-head h3 {
  margin: 0 0 4px;
  font-size: 22px;
}

.lab-head .lab-sub {
  font-size: 13px;
  color: var(--text-2);
  margin: 0;
}

.lab-body {
  padding: 20px 22px 22px;
}

.lab-broken {
  border-left: 3px solid var(--error);
  padding: 2px 0 2px 14px;
  margin: 0 0 18px;
  font-size: 15px;
}

.lab-broken .label {
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--error);
  display: block;
}

.lab-grid {
  display: grid;
  grid-template-columns: minmax(0, 0.9fr) minmax(0, 1.1fr);
  gap: 22px;
  align-items: start;
}

.lab-grid > * {
  min-width: 0;
}

.lab-grid h4 {
  margin-top: 0;
  font-size: 13px;
  font-family: var(--mono);
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--text-3);
}

.lab-grid ul {
  font-size: 14px;
  padding-left: 18px;
}

.lab-grid li {
  margin-bottom: 7px;
}

.task-list {
  list-style: none;
  padding-left: 0;
  counter-reset: task;
}

.task-list li {
  counter-increment: task;
  position: relative;
  padding-left: 28px;
  font-size: 14px;
  margin-bottom: 9px;
}

.task-list li::before {
  content: counter(task);
  position: absolute;
  left: 0;
  top: 3px;
  font-family: var(--mono);
  font-size: 10px;
  color: var(--accent);
  border: 1px solid var(--accent);
  border-radius: 50%;
  width: 18px;
  height: 18px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
}

.pathline {
  font-family: var(--mono);
  font-size: 11.5px;
  color: var(--text-2);
  background: var(--bg-soft);
  border: 1px solid var(--border);
  border-radius: 5px;
  padding: 5px 8px;
  display: flex;
  gap: 10px;
  align-items: center;
  overflow-wrap: anywhere;
  margin: 8px 0 12px;
}

.pathline code {
  font-family: var(--mono);
  font-size: 11.5px;
  color: var(--text);
  min-width: 0;
  overflow-wrap: anywhere;
}

.lab-grid code,
.lab-broken code,
.lab-foot code {
  overflow-wrap: anywhere;
}

.lab-preview {
  border: 0;
  border-radius: 7px;
  background: var(--bg-soft);
  max-width: 100%;
  max-height: 300px;
  overflow: auto;
}

.lab-preview pre {
  margin: 0;
  padding: 12px 14px;
  font-family: var(--mono);
  font-size: 12px;
  line-height: 1.6;
  color: var(--code-fg);
  white-space: pre;
}

.lab-actions {
  display: flex;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
  margin-top: 12px;
}

.lab-status {
  font-family: var(--mono);
  font-size: 11px;
  color: var(--text-3);
}

.lab-results {
  margin-top: 14px;
  border-top: 1px solid var(--border);
  padding-top: 12px;
}

.lab-results[hidden] {
  display: none;
}

.result-badge {
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  padding: 3px 8px;
  border-radius: 4px;
  display: inline-block;
  margin-bottom: 8px;
}

.result-badge.pass {
  background: #e9f7ef;
  color: var(--success);
}

.result-badge.fail {
  background: #fdf0ee;
  color: var(--error);
}

.result-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 12.8px;
  table-layout: fixed;
}

.result-table th,
.result-table td {
  text-align: left;
  padding: 6px 8px;
  border-bottom: 1px solid var(--border);
  vertical-align: top;
  overflow-wrap: anywhere;
}

.result-table th {
  font-family: var(--mono);
  font-size: 10.5px;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--text-3);
  font-weight: 500;
}

.result-table td:first-child {
  width: 42%;
}

details.hints {
  margin-top: 16px;
  font-size: 14px;
}

details.hints summary {
  cursor: pointer;
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--accent);
  padding: 4px 0;
}

details.hints .hint {
  border-left: 2px solid var(--border-strong);
  padding: 4px 0 4px 12px;
  margin: 8px 0;
  color: var(--text-2);
}

details.hints .hint b {
  color: var(--text);
}

.lab-foot {
  margin-top: 16px;
  font-size: 12.5px;
  color: var(--text-3);
}

.lab-foot code {
  font-family: var(--mono);
  font-size: 11.5px;
  background: var(--bg-soft);
  padding: 1px 5px;
  border-radius: 3px;
}

/* ---------- recap / next ---------- */
.recap {
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--bg-soft);
  padding: 16px 18px;
  margin: 22px 0;
  font-size: 14px;
}

.recap h4 {
  margin: 0 0 8px;
  font-size: 12px;
  font-family: var(--mono);
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--text-3);
}

.recap ul {
  margin: 0;
  padding-left: 18px;
  color: var(--text-2);
}

.nextbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
  padding: 14px 0;
  border-top: 1px solid var(--border);
  font-size: 13px;
  color: var(--text-3);
}

.nextbar a {
  font-family: var(--mono);
  font-size: 11.5px;
}

/* ---------- footer ---------- */
footer {
  border-top: 1px solid var(--border);
  padding: 44px 0 70px;
  margin-top: 30px;
}

footer .wrap {
  color: var(--text-3);
  font-size: 13px;
}

footer h3 {
  font-family: var(--display);
  color: var(--text);
  font-size: 20px;
  margin: 0 0 10px;
}

footer .readorder {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 6px 26px;
  font-size: 13.5px;
  margin: 16px 0 22px;
}

footer .readorder a {
  color: var(--text-2);
  text-decoration: none;
  border-bottom: 1px solid var(--border);
  padding: 5px 0;
}

footer .readorder a:hover {
  color: var(--accent);
}

.smallprint {
  font-size: 11.5px;
  font-family: var(--mono);
  color: var(--text-3);
  line-height: 1.7;
  border-top: 1px solid var(--border);
  padding-top: 18px;
}

/* ---------- responsive ---------- */
@media (max-width: 1080px) {
  .shell {
    grid-template-columns: 210px minmax(0, 1fr);
  }
  .rail {
    padding-left: 16px;
    padding-right: 12px;
  }
}

@media (max-width: 900px) {
  .shell {
    display: block;
  }
  .rail {
    display: none;
  }
  .hero-grid {
    grid-template-columns: 1fr;
  }
  .lab-grid {
    grid-template-columns: minmax(0, 1fr);
    gap: 16px;
  }
  .wrap {
    padding: 0 22px;
  }
  .module-num {
    font-size: 48px;
  }
}

@media (max-width: 640px) {
  body {
    font-size: 16px;
  }
  .topnav {
    padding: 0 14px;
    gap: 10px;
  }
  .navmeta {
    display: none;
  }
  .navlinks a {
    font-size: 12px;
    padding: 5px 6px;
  }
  .brand {
    font-size: 13.5px;
  }
  .wrap {
    padding: 0 16px;
  }
  .hero {
    padding-top: 40px;
  }
  .hero .lede {
    font-size: 17px;
  }
  .translate {
    grid-template-columns: 1fr;
  }
  .translate .t-code {
    border-right: 0;
    border-bottom: 1px solid var(--border);
  }
  .gate-step {
    padding: 15px 14px;
  }
  .gate-time {
    display: none;
  }
  .timechip {
    display: block;
    margin: 6px 0 0;
    width: fit-content;
  }
  .lab-body,
  .lab-head {
    padding-left: 15px;
    padding-right: 15px;
  }
  footer .readorder {
    grid-template-columns: 1fr;
  }
  .result-table td:first-child {
    width: 48%;
  }
}