:root {
  --font-body: -apple-system, BlinkMacSystemFont, 'SF Pro Text', 'Helvetica Neue', Helvetica, Arial, sans-serif;
  --font-heading: -apple-system, BlinkMacSystemFont, 'SF Pro Display', 'Helvetica Neue', Helvetica, Arial, sans-serif;
  --font-mono: 'SF Mono', 'Fira Code', 'Consolas', 'Menlo', monospace;
  --color-text: #1d1d1f;
  --color-muted: #6e6e73;
  --color-accent: #0078d4;
  --color-accent-light: #e8f4fd;
  --color-bg: #fff;
  --color-code-bg: #f5f5f7;
  --color-border: #d2d2d7;
  --color-callout-bg: #f5f5f7;
  --color-card-bg: #fbfbfd;
  --color-success: #34c759;
  --color-warning: #ff9f0a;
  --color-danger: #ff3b30;
  --max-width: 740px;
  --line-height: 1.58;
  --radius: 12px;
  --shadow-card: 0 1px 3px rgba(0,0,0,0.04), 0 4px 12px rgba(0,0,0,0.06);
}

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

body {
  font-family: var(--font-body);
  font-size: 17px;
  line-height: var(--line-height);
  color: var(--color-text);
  background: var(--color-bg);
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 3rem 1.5rem 4rem;
}

h1 {
  font-family: var(--font-heading);
  font-size: 2.4rem;
  font-weight: 700;
  letter-spacing: -0.03em;
  margin-bottom: 0.5rem;
}

h2 {
  font-family: var(--font-heading);
  font-size: 1.6rem;
  font-weight: 600;
  margin-top: 3rem;
  margin-bottom: 1rem;
}

h3 {
  font-family: var(--font-heading);
  font-size: 1.2rem;
  font-weight: 600;
  margin-top: 2rem;
  margin-bottom: 0.75rem;
}

p { margin-bottom: 1.2rem; }

a { color: var(--color-accent); text-decoration: none; }
a:hover { text-decoration: underline; }

code {
  font-family: var(--font-mono);
  font-size: 0.82rem;
  background: var(--color-code-bg);
  padding: 0.15em 0.4em;
  border-radius: 4px;
}

pre {
  position: relative;
  font-family: var(--font-mono);
  font-size: 0.8rem;
  line-height: 1.5;
  background: var(--color-code-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 1.25rem 1.5rem;
  overflow-x: auto;
  margin-bottom: 1.5rem;
}

pre code {
  background: none;
  padding: 0;
  font-size: inherit;
}

/* Lesson meta */
.lesson-meta {
  color: var(--color-muted);
  font-size: 0.9rem;
  margin-bottom: 2.5rem;
}

/* Callouts */
.callout {
  background: var(--color-callout-bg);
  border-left: 4px solid var(--color-border);
  border-radius: var(--radius);
  padding: 1.25rem 1.5rem;
  margin-bottom: 1.5rem;
}
.callout.tip { border-left-color: var(--color-success); }
.callout.warning { border-left-color: var(--color-warning); }
.callout.danger { border-left-color: var(--color-danger); }
.callout-title {
  font-weight: 600;
  font-size: 0.85rem;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  margin-bottom: 0.5rem;
}
.callout.tip .callout-title { color: var(--color-success); }
.callout.warning .callout-title { color: var(--color-warning); }
.callout.danger .callout-title { color: var(--color-danger); }
.callout p:last-child { margin-bottom: 0; }

/* Primary source */
.primary-source {
  background: var(--color-accent-light);
  border-radius: var(--radius);
  padding: 1.25rem 1.5rem;
  margin: 2rem 0;
}
.primary-source-label {
  font-weight: 600;
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: var(--color-accent);
  margin-bottom: 0.4rem;
}
.primary-source p { margin-bottom: 0; }

/* Ask teacher */
.ask-teacher {
  background: var(--color-card-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 1.25rem 1.5rem;
  margin: 2.5rem 0;
  font-size: 0.95rem;
}

/* Quiz */
.quiz {
  background: var(--color-card-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 1.5rem;
  margin: 2rem 0;
}
.quiz-question {
  font-weight: 600;
  margin-bottom: 1rem;
}
.quiz-options {
  list-style: none;
  padding: 0;
}
.quiz-options li {
  padding: 0.75rem 1rem;
  margin-bottom: 0.5rem;
  border: 1px solid var(--color-border);
  border-radius: 8px;
  cursor: pointer;
  transition: background 0.15s, border-color 0.15s;
}
.quiz-options li:hover { background: var(--color-code-bg); }
.quiz-options li.correct {
  background: #e8f8ed;
  border-color: var(--color-success);
  cursor: default;
}
.quiz-options li.incorrect {
  background: #fef2f2;
  border-color: var(--color-danger);
  cursor: default;
}
.quiz-feedback {
  display: none;
  margin-top: 1rem;
  padding: 0.75rem 1rem;
  border-radius: 8px;
  font-size: 0.9rem;
}
.quiz-feedback.correct {
  background: #e8f8ed;
  color: #1a7f37;
}
.quiz-feedback.incorrect {
  background: #fef2f2;
  color: #cf222e;
}
.quiz-feedback.show { display: block; }

/* Tables */
table {
  width: 100%;
  border-collapse: collapse;
  margin-bottom: 1.5rem;
  font-size: 0.9rem;
}
th {
  text-align: left;
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: var(--color-muted);
  padding: 0.75rem 1rem;
  border-bottom: 2px solid var(--color-border);
}
td {
  padding: 0.75rem 1rem;
  border-bottom: 1px solid var(--color-border);
}

/* Diagram */
.diagram {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  line-height: 1.4;
  background: var(--color-card-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 1.5rem;
  margin: 1.5rem 0;
  overflow-x: auto;
  white-space: pre;
}

/* Navigation */
/* Top navigation — hover pattern adapted from learn-cloudflare */
.lesson-top-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 2rem;
  font-size: 0.88rem;
}
.lesson-top-nav a {
  color: var(--color-accent);
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
  font-weight: 400;
  text-decoration: none;
  transition: color 0.2s;
}
.lesson-back-top:hover,
.lesson-next-top:hover { text-decoration: underline; color: #005a9e; }
.lesson-top-nav svg { transition: transform 0.2s; }
/* chevrons slide toward their travel direction on hover */
.lesson-back-top:hover svg { transform: translateX(-2px); }
.lesson-next-top:hover svg { transform: translateX(2px); }
.lesson-home-top {
  color: var(--color-muted);
  opacity: 0.6;
  transition: opacity 0.2s, color 0.2s;
}
.lesson-home-top:hover { opacity: 1; color: var(--color-accent); }

/* Bottom navigation */
.lesson-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: 4rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--color-border);
  font-family: var(--font-heading);
  font-size: 0.88rem;
}
.lesson-nav a {
  color: var(--color-accent);
  font-weight: 500;
  text-decoration: none;
  transition: color 0.2s;
}
.lesson-nav a:hover { text-decoration: underline; color: #005a9e; }
/* only the arrow glyph slides on hover — no button styling */
.lesson-nav-next, .lesson-nav-prev { display: inline-flex; align-items: center; gap: 0.3rem; }
.lesson-nav-prev .arrow, .lesson-nav-next .arrow { transition: transform 0.2s; display: inline-block; }
.lesson-nav-prev:hover .arrow { transform: translateX(-3px); }
.lesson-nav-next:hover .arrow { transform: translateX(3px); }
.lesson-nav-home {
  display: flex;
  align-items: center;
  color: var(--color-muted);
  opacity: 0.6;
  transition: opacity 0.2s, color 0.2s;
}
.lesson-nav-home:hover { opacity: 1; color: var(--color-accent); }

/* Lesson index */
.lesson-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1rem;
  margin-top: 1.5rem;
}
.lesson-card {
  display: block;
  background: var(--color-card-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 1.25rem 1.5rem;
  transition: box-shadow 0.15s, border-color 0.15s;
  text-decoration: none;
  color: var(--color-text);
}
.lesson-card:hover {
  box-shadow: var(--shadow-card);
  border-color: var(--color-accent);
  text-decoration: none;
}
.lesson-card-number {
  font-size: 0.75rem;
  color: var(--color-muted);
  text-transform: uppercase;
  letter-spacing: 0.04em;
}
.lesson-card-title {
  font-weight: 600;
  margin-top: 0.25rem;
}
.lesson-card-desc {
  font-size: 0.9rem;
  color: var(--color-muted);
  margin-top: 0.3rem;
}
.section-label {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--color-muted);
  margin-top: 2rem;
  margin-bottom: 0.5rem;
  font-weight: 600;
}

/* Responsive */
@media (max-width: 600px) {
  body { font-size: 16px; padding: 2rem 1rem 3rem; }
  h1 { font-size: 1.8rem; }
  h2 { font-size: 1.3rem; }
  pre { padding: 1rem; font-size: 0.75rem; }
}

/* Print */
@media print {
  body { max-width: none; padding: 0; }
  .lesson-top-nav, .lesson-nav { display: none; }
  a::after { content: ' (' attr(href) ')'; font-size: 0.8em; color: var(--color-muted); }
  .callout, .quiz, .primary-source { box-shadow: none; border: 1px solid var(--color-border); }
}