/* ===== Design tokens ===== */
:root {
  --bg: #FAFAF8;
  --bg-subtle: #F3F2EE;
  --text: #1A1A1A;
  --text-muted: #6B6B6B;
  --accent: #1E4FD8;
  --accent-hover: #1A45BE;
  --border: #E8E7E3;
  --success: #1F9D57;

  --font-sans: "Inter", "Noto Sans SC", "Source Han Sans SC", -apple-system, sans-serif;
  --font-mono: "JetBrains Mono", ui-monospace, "SF Mono", Menlo, monospace;

  --ease-out-expo: cubic-bezier(0.16, 1, 0.3, 1);

  --space-1: 8px;
  --space-2: 16px;
  --space-3: 24px;
  --space-4: 32px;
  --space-6: 48px;
  --space-8: 64px;
  --space-12: 96px;
  --space-16: 128px;
}

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  scroll-behavior: smooth;
}

body {
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

/* ===== Typography scale (modular, ratio 1.333) ===== */
.eyebrow {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--text-muted);
  letter-spacing: 0.05em;
  text-transform: none;
}

.h1 {
  font-size: 3.157rem;
  font-weight: 700;
  letter-spacing: 0.02em;
  line-height: 1.15;
}

.h2 {
  font-size: 2.369rem;
  font-weight: 700;
  letter-spacing: 0.02em;
  line-height: 1.2;
}

.body-text {
  font-size: 1.125rem;
  color: var(--text-muted);
  line-height: 1.7;
}

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

/* ===== Reduced motion ===== */
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
}

/* ===== Nav ===== */
.site-nav {
  position: sticky;
  top: 0;
  z-index: 10;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--space-2) var(--space-4);
  border-bottom: 1px solid transparent;
  background: transparent;
  transition: background-color 0.3s var(--ease-out-expo), border-color 0.3s var(--ease-out-expo);
}

/* .surfaced is applied once, shortly after page load (per spec: the nav
   materializes "as the page loads, not instantly") — see the
   `nav.classList.add('surfaced')` call in script.js Task 2 Step 4's nav
   block. It stays applied afterward regardless of scroll position; this
   class name (not `.scrolled`) reflects that its trigger is load-timing,
   not scroll position. */
.site-nav.surfaced {
  background: rgba(250, 250, 248, 0.8);
  backdrop-filter: blur(8px);
  border-bottom-color: var(--border);
}

.nav-logo {
  font-size: 1rem;
  font-weight: 500;
  color: var(--text);
}

.nav-links {
  display: flex;
  align-items: center;
  gap: var(--space-3);
}

.nav-link {
  color: var(--text-muted);
  text-decoration: none;
  font-size: 0.9375rem;
}

.nav-link:hover {
  color: var(--text);
}

.nav-cta {
  background: var(--accent);
  color: white;
  padding: 8px 20px;
  border-radius: 6px;
  text-decoration: none;
  font-size: 0.9375rem;
  font-weight: 500;
  transition: background-color 0.2s var(--ease-out-expo);
}

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

/* ===== Hero ===== */
.hero {
  position: relative;
  padding: var(--space-16) var(--space-4) var(--space-12);
}

/* Hairline divider that draws in left-to-right (per spec) once the hero
   sequence completes, instead of being a static border from page load. */
.hero::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  width: 100%;
  height: 1px;
  background: var(--border);
  transform: scaleX(0);
  transform-origin: left;
  transition: transform 0.6s var(--ease-out-expo);
}

.hero.divider-drawn::after {
  transform: scaleX(1);
}

.hero-inner {
  max-width: 720px;
  margin: 0 auto;
}

.hero-demo {
  margin-top: var(--space-6);
  margin-bottom: var(--space-4);
  min-height: 80px;
}

.hero-cursor {
  color: var(--accent);
  font-size: 1.25rem;
  animation: blink 1.06s steps(1) infinite;
}

@keyframes blink {
  0%, 49% { opacity: 1; }
  50%, 100% { opacity: 0; }
}

.hero-typed {
  color: var(--text-muted);
  font-size: 1.125rem;
}

.hero-result {
  display: none;
  align-items: center;
  gap: 8px;
  margin-top: var(--space-2);
  padding: 10px 16px;
  background: var(--bg-subtle);
  border: 1px solid var(--border);
  border-radius: 6px;
  font-size: 0.9375rem;
  color: var(--text);
  width: fit-content;
  opacity: 0;
  transform: translateY(8px);
  transition: opacity 0.4s var(--ease-out-expo), transform 0.4s var(--ease-out-expo);
}

.hero-result.visible {
  display: flex;
  opacity: 1;
  transform: translateY(0);
}

.hero-result-check {
  color: var(--success);
  font-weight: 700;
}

.hero-headline {
  opacity: 0;
  transform: translateY(8px);
  transition: opacity 0.5s var(--ease-out-expo), transform 0.5s var(--ease-out-expo);
}

.hero-headline.visible {
  opacity: 1;
  transform: translateY(0);
}

.hero-subhead {
  margin-top: var(--space-2);
  max-width: 560px;
  opacity: 0;
  transition: opacity 0.5s var(--ease-out-expo);
}

.hero-subhead.visible {
  opacity: 1;
}

.nav-cta.cursor-landed .nav-cta-cursor {
  animation: blink 1.06s steps(1) infinite;
}

/* ===== Diff section ===== */
.diff-section {
  padding: var(--space-16) var(--space-4);
  border-bottom: 1px solid var(--border);
}

.diff-inner {
  max-width: 900px;
  margin: 0 auto;
}

.diff-columns {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-6);
  margin-top: var(--space-4);
}

@media (max-width: 720px) {
  .diff-columns {
    grid-template-columns: 1fr;
  }
}

.diff-header {
  font-size: 0.9375rem;
  font-weight: 500;
  margin-bottom: var(--space-2);
  color: var(--text-muted);
}

.diff-header-accent {
  color: var(--accent);
}

.diff-line {
  font-size: 0.9375rem;
  padding: 4px 0;
}

.diff-line-removed {
  color: var(--text-muted);
  text-decoration: line-through;
}

.diff-line-added {
  color: var(--accent);
}

/* ===== Tools section ===== */
.tools-section {
  padding: var(--space-16) var(--space-4);
  border-bottom: 1px solid var(--border);
}

.tools-inner {
  max-width: 640px;
  margin: 0 auto;
}

.tools-timeline {
  position: relative;
  margin-top: var(--space-6);
  padding-left: var(--space-4);
}

.tools-caption {
  margin-top: var(--space-6);
  padding-left: var(--space-4);
}

.tools-rule {
  position: absolute;
  left: 4px;
  top: 6px;
  bottom: 6px;
  width: 1px;
  background: var(--border);
}

.tool-item {
  position: relative;
  display: flex;
  align-items: center;
  gap: var(--space-2);
  padding: 10px 0;
}

/* Subtle grouping (per spec: "may be grouped subtly by category") — the
   first item of the "issue" group and the first item of the "pr" group
   each get a bit of extra top spacing via the adjacent-sibling combinator,
   reading as a soft break between the repo/issue/pr clusters without a
   hard card boundary. This is the actual (previously unused) purpose of
   each .tool-item's data-group attribute set in this task's HTML. */
.tool-item[data-group="repo"] + .tool-item[data-group="issue"],
.tool-item[data-group="issue"] + .tool-item[data-group="pr"] {
  margin-top: var(--space-2);
}

.tool-dot {
  position: absolute;
  left: calc(-1 * var(--space-4) + 0px);
  width: 9px;
  height: 9px;
  border-radius: 50%;
  border: 1.5px solid var(--border);
  background: var(--bg);
  transition: background-color 0.3s var(--ease-out-expo), border-color 0.3s var(--ease-out-expo), transform 0.3s var(--ease-out-expo);
}

.tool-label {
  color: var(--text-muted);
  font-size: 1rem;
  transition: color 0.3s var(--ease-out-expo);
}

.tool-item.visible .tool-dot {
  background: var(--accent);
  border-color: var(--accent);
  transform: scale(1.15);
}

.tool-item.visible .tool-label {
  color: var(--text);
}

/* ===== Security section ===== */
.security-section {
  padding: var(--space-16) var(--space-4);
  border-bottom: 1px solid var(--border);
  display: flex;
  justify-content: center;
}

.security-badge {
  max-width: 480px;
  text-align: center;
  padding: var(--space-6) var(--space-4);
  border: 1px solid var(--border);
  border-radius: 8px;
  transition: border-color 0.2s var(--ease-out-expo), transform 0.2s var(--ease-out-expo);
}

.security-badge:hover {
  border-color: var(--accent);
  transform: scale(1.02);
}

.security-lock {
  font-size: 1.75rem;
  display: block;
  margin-bottom: var(--space-2);
}

.security-title {
  font-size: 1.125rem;
  font-weight: 600;
  margin-bottom: var(--space-1);
}

.security-caption {
  font-size: 0.9375rem;
  color: var(--text-muted);
}

/* ===== Tutorial section ===== */
.tutorial-section {
  padding: var(--space-16) var(--space-4);
  border-bottom: 1px solid var(--border);
}

.tutorial-inner {
  max-width: 960px;
  margin: 0 auto;
}

.tutorial-steps {
  position: relative;
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--space-6);
  margin-top: var(--space-6);
}

@media (max-width: 720px) {
  .tutorial-steps {
    grid-template-columns: 1fr;
  }
}

/* Two stacked lines: a static gray track (always visible, shows the full
   path) and an indigo fill line that grows left-to-right via scaleX — this
   is the actual "relay baton" motion the spec describes, driven by a single
   timed animation rather than per-step independent triggers (which, on the
   desktop 3-column grid, would fire near-simultaneously and never look
   sequential). */
.tutorial-relay-line {
  position: absolute;
  top: 15px;
  left: calc(16.66% + 15px);
  right: calc(16.66% + 15px);
  height: 1px;
  background: var(--border);
  z-index: 0;
}

.tutorial-relay-fill {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: var(--accent);
  transform: scaleX(0);
  transform-origin: left;
  transition: transform 1.2s var(--ease-out-expo);
}

.tutorial-relay-line.running .tutorial-relay-fill {
  transform: scaleX(1);
}

@media (max-width: 720px) {
  .tutorial-relay-line {
    display: none;
  }
}

.tutorial-step {
  position: relative;
  z-index: 1;
}

.step-number {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 32px;
  height: 32px;
  border-radius: 50%;
  border: 1.5px solid var(--border);
  color: var(--text-muted);
  font-weight: 600;
  background: var(--bg);
  transition: background-color 0.3s var(--ease-out-expo), border-color 0.3s var(--ease-out-expo), color 0.3s var(--ease-out-expo);
}

.tutorial-step.visible .step-number {
  background: var(--accent);
  border-color: var(--accent);
  color: white;
}

.step-icon {
  display: block;
  width: 28px;
  height: 28px;
  margin-top: var(--space-2);
  color: var(--text-muted);
  transition: color 0.3s var(--ease-out-expo);
}

.tutorial-step.visible .step-icon {
  color: var(--accent);
}

.step-title {
  margin-top: var(--space-2);
  font-size: 1.125rem;
  font-weight: 600;
}

.step-desc {
  margin-top: var(--space-1);
  font-size: 0.9375rem;
  color: var(--text-muted);
  line-height: 1.6;
}

.step-desc code {
  background: var(--bg-subtle);
  padding: 2px 6px;
  border-radius: 4px;
  font-size: 0.875rem;
}

/* ===== Closing CTA ===== */
.closing-cta {
  padding: var(--space-16) var(--space-4);
  text-align: center;
}

.closing-cta-inner {
  max-width: 560px;
  margin: 0 auto;
}

.closing-cta-button {
  display: inline-block;
  margin-top: var(--space-4);
  background: var(--accent);
  color: white;
  padding: 14px 32px;
  border-radius: 8px;
  text-decoration: none;
  font-size: 1.0625rem;
  font-weight: 500;
  transition: background-color 0.2s var(--ease-out-expo);
}

.closing-cta-button:hover {
  background: var(--accent-hover);
}

.closing-cta-endpoint {
  margin-top: var(--space-4);
  font-size: 0.875rem;
  color: var(--text-muted);
}