@import url('https://fonts.googleapis.com/css2?family=Source+Serif+4:ital,opsz,wght@0,8..60,300;0,8..60,400;0,8..60,600;1,8..60,300;1,8..60,400&family=DM+Sans:wght@300;400;500&family=DM+Mono:wght@400;500&display=swap');

:root {
  --serif: 'Source Serif 4', Georgia, serif;
  --sans: 'DM Sans', system-ui, sans-serif;
  --mono: 'DM Mono', 'Courier New', monospace;

  --text-primary: #1a1714;
  --text-secondary: #6b6560;
  --text-tertiary: #9e9890;
  --text-inverse: #fff;

  --bg-primary: #faf9f7;
  --bg-secondary: #f3f0ea;
  --bg-tertiary: #ede9e0;
  --bg-code: #edeae2;

  --accent: #1a1714;
  --accent-soft: #e4dfd4;
  --border: #e4dfd4;
  --border-strong: #cec8bc;

  --tag-fundamental-bg: #eef0fa;
  --tag-fundamental-text: #3558c4;
  --tag-advanced-bg: #fdf0e8;
  --tag-advanced-text: #b84010;

  --max-width: 720px;
  --wide-width: 1100px;
}

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

html { font-size: 16px; -webkit-font-smoothing: antialiased; scroll-behavior: smooth; }

body {
  font-family: var(--serif);
  background: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.75;
}

/* ── Typography ── */
h1, h2, h3, h4 { font-family: var(--serif); font-weight: 600; line-height: 1.3; }
h1 { font-size: 2.4rem; letter-spacing: -0.02em; }
h2 { font-size: 1.7rem; letter-spacing: -0.01em; margin: 2.5rem 0 1rem; scroll-margin-top: 72px; }
h3 { font-size: 1.2rem; margin: 2rem 0 0.6rem; }

/* ── Heading anchors ── */
.heading-anchor {
  opacity: 0;
  margin-left: 10px;
  font-size: 0.75em;
  color: var(--text-tertiary);
  text-decoration: none;
  font-weight: 400;
  font-family: var(--sans);
  transition: opacity 0.15s;
  vertical-align: middle;
}
h2:hover .heading-anchor { opacity: 1; }
h4 { font-size: 1rem; font-weight: 500; margin: 1.5rem 0 0.4rem; }
p  { font-size: 1.1rem; margin-bottom: 1.25rem; color: var(--text-primary); }
a  { color: var(--text-primary); text-decoration: underline; text-underline-offset: 3px; }
a:hover { opacity: 0.7; }
strong { font-weight: 600; }
em { font-style: italic; }

/* ── Layout ── */
.container { max-width: var(--max-width); margin: 0 auto; padding: 0 24px; }
.container-wide { max-width: var(--wide-width); margin: 0 auto; padding: 0 24px; }

/* ── Nav ── */
nav {
  border-bottom: 1px solid var(--border);
  padding: 16px 0;
  position: sticky;
  top: 0;
  background: rgba(250, 249, 247, 0.95);
  backdrop-filter: blur(8px);
  z-index: 100;
}
.nav-inner {
  max-width: var(--wide-width);
  margin: 0 auto;
  padding: 0 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
}
.nav-logo {
  font-family: var(--sans);
  font-size: 0.9rem;
  font-weight: 500;
  text-decoration: none;
  color: var(--text-primary);
  letter-spacing: 0.02em;
  white-space: nowrap;
}
.nav-links {
  display: flex;
  gap: 24px;
  list-style: none;
  flex-wrap: wrap;
}
.nav-links a {
  font-family: var(--sans);
  font-size: 0.85rem;
  color: var(--text-secondary);
  text-decoration: none;
  transition: color 0.15s;
}
.nav-links a:hover { color: var(--text-primary); }
.nav-links a.active { color: var(--text-primary); font-weight: 500; }

/* ── Hero ── */
.hero {
  padding: 80px 0 64px;
  border-bottom: 1px solid var(--border);
}
.hero-eyebrow {
  font-family: var(--sans);
  font-size: 0.8rem;
  font-weight: 500;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--text-tertiary);
  margin-bottom: 16px;
}
.hero h1 { margin-bottom: 20px; }
.hero-lead {
  font-size: 1.25rem;
  color: var(--text-secondary);
  font-weight: 300;
  max-width: 560px;
  line-height: 1.6;
  margin-bottom: 32px;
}
.hero-meta {
  font-family: var(--sans);
  font-size: 0.85rem;
  color: var(--text-tertiary);
  display: flex;
  align-items: center;
  gap: 16px;
  flex-wrap: wrap;
}
.hero-meta a { color: var(--text-secondary); }

/* ── Article body ── */
.article-body { padding: 56px 0 80px; }
.article-body > * + * { margin-top: 0; }

/* ── Tags ── */
.tag {
  display: inline-block;
  font-family: var(--sans);
  font-size: 0.72rem;
  font-weight: 500;
  padding: 3px 8px;
  border-radius: 4px;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  vertical-align: middle;
  margin-left: 8px;
}
.tag-fundamental { background: var(--tag-fundamental-bg); color: var(--tag-fundamental-text); }
.tag-advanced    { background: var(--tag-advanced-bg);    color: var(--tag-advanced-text); }

/* ── Code ── */
code {
  font-family: var(--mono);
  font-size: 0.88em;
  background: var(--bg-code);
  padding: 2px 6px;
  border-radius: 4px;
  color: #c7254e;
}
pre {
  background: var(--bg-code);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 20px 24px;
  overflow-x: auto;
  margin: 1.5rem 0;
}
pre code {
  background: none;
  padding: 0;
  color: var(--text-primary);
  font-size: 0.88rem;
  line-height: 1.7;
}

/* ── Blockquote / callout ── */
blockquote {
  border-left: 3px solid var(--text-primary);
  padding: 4px 0 4px 24px;
  margin: 2rem 0;
  font-style: italic;
  color: var(--text-secondary);
  font-size: 1.15rem;
}
.callout {
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 20px 24px;
  margin: 2rem 0;
  font-size: 1rem;
}
.callout-label {
  font-family: var(--sans);
  font-size: 0.75rem;
  font-weight: 500;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--text-tertiary);
  margin-bottom: 8px;
}
.insight {
  background: #fdf7ed;
  border-left: 3px solid #d97706;
  border-radius: 0 8px 8px 0;
  padding: 16px 20px;
  margin: 2rem 0;
  font-size: 1rem;
}
.insight-label {
  font-family: var(--sans);
  font-size: 0.72rem;
  font-weight: 500;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: #92400e;
  margin-bottom: 6px;
}

/* ── Q&A quote ── */
.qa-block {
  margin: 2rem 0;
  border: 1px solid var(--border);
  border-radius: 8px;
  overflow: hidden;
}
.qa-row {
  display: flex;
  gap: 0;
}
.qa-row + .qa-row { border-top: 1px solid var(--border); }
.qa-role {
  font-family: var(--sans);
  font-size: 0.72rem;
  font-weight: 500;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  padding: 14px 16px;
  min-width: 100px;
  background: var(--bg-secondary);
  color: var(--text-tertiary);
  border-right: 1px solid var(--border);
  display: flex;
  align-items: flex-start;
  padding-top: 16px;
}
.qa-role.you { color: #2563eb; background: #f0f5ff; }
.qa-text {
  padding: 14px 20px;
  font-size: 1rem;
  line-height: 1.65;
  flex: 1;
}

/* ── Divider ── */
.divider {
  border: none;
  border-top: 1px solid var(--border);
  margin: 3rem 0;
}
.section-divider {
  display: flex;
  align-items: center;
  gap: 16px;
  margin: 3rem 0;
  color: var(--text-tertiary);
  font-family: var(--sans);
  font-size: 0.8rem;
}
.section-divider::before,
.section-divider::after {
  content: '';
  flex: 1;
  border-top: 1px solid var(--border);
}

/* ── Cards grid (landing page) ── */
.cards-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 1px;
  background: var(--border);
  border: 1px solid var(--border);
  border-radius: 12px;
  overflow: hidden;
  margin: 2.5rem 0;
}
.card {
  background: var(--bg-primary);
  padding: 32px;
  text-decoration: none;
  color: inherit;
  display: block;
  transition: background 0.15s;
}
.card:hover { background: var(--bg-secondary); }
.card-eyebrow {
  font-family: var(--sans);
  font-size: 0.72rem;
  font-weight: 500;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--text-tertiary);
  margin-bottom: 12px;
}
.card h3 {
  font-size: 1.1rem;
  margin: 0 0 10px;
  font-weight: 600;
}
.card p {
  font-size: 0.95rem;
  color: var(--text-secondary);
  margin: 0;
  line-height: 1.55;
}
.card-arrow {
  font-size: 1.2rem;
  margin-top: 16px;
  color: var(--text-tertiary);
  display: block;
}

/* ── Table ── */
table {
  width: 100%;
  border-collapse: collapse;
  font-family: var(--sans);
  font-size: 0.9rem;
  margin: 1.5rem 0;
}
th {
  text-align: left;
  font-weight: 500;
  padding: 10px 14px;
  border-bottom: 2px solid var(--border-strong);
  color: var(--text-secondary);
  font-size: 0.82rem;
  letter-spacing: 0.04em;
  text-transform: uppercase;
}
td {
  padding: 10px 14px;
  border-bottom: 1px solid var(--border);
  vertical-align: top;
  line-height: 1.55;
}
td code { font-size: 0.82rem; }
tr:last-child td { border-bottom: none; }

/* ── Diagram container ── */
.diagram {
  margin: 2rem 0;
  border: 1px solid var(--border);
  border-radius: 8px;
  overflow: hidden;
  background: var(--bg-secondary);
}
.diagram-label {
  font-family: var(--sans);
  font-size: 0.78rem;
  color: var(--text-tertiary);
  padding: 10px 16px;
  border-bottom: 1px solid var(--border);
  background: var(--bg-tertiary);
  letter-spacing: 0.04em;
}
.diagram svg { display: block; width: 100%; }

/* ── TOC ── */
.toc {
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 24px 28px;
  margin: 2rem 0;
}
.toc-title {
  font-family: var(--sans);
  font-size: 0.78rem;
  font-weight: 500;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--text-tertiary);
  margin-bottom: 12px;
}
.toc ol { padding-left: 20px; }
.toc li { margin-bottom: 6px; }
.toc a {
  font-family: var(--sans);
  font-size: 0.9rem;
  color: var(--text-secondary);
  text-decoration: none;
}
.toc a:hover { color: var(--text-primary); }

/* ── Author note ── */
.author-note {
  display: flex;
  gap: 20px;
  align-items: flex-start;
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 28px;
  margin: 2.5rem 0;
}
.author-avatar {
  flex-shrink: 0;
  width: 48px;
  height: 48px;
  border-radius: 50%;
  background: var(--bg-tertiary);
  border: 1px solid var(--border-strong);
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--sans);
  font-size: 0.8rem;
  font-weight: 500;
  color: var(--text-secondary);
  letter-spacing: 0.04em;
}
.author-body { flex: 1; }
.author-name {
  font-family: var(--sans);
  font-size: 0.95rem;
  font-weight: 500;
  color: var(--text-primary);
  margin-bottom: 10px;
  display: flex;
  align-items: center;
  gap: 10px;
}
.author-linkedin {
  font-size: 0.78rem;
  font-weight: 400;
  color: var(--text-tertiary);
  text-decoration: none;
  letter-spacing: 0.02em;
}
.author-linkedin:hover { color: var(--text-secondary); }
.author-bio {
  font-size: 0.95rem;
  color: var(--text-secondary);
  line-height: 1.65;
  margin-bottom: 8px;
}
@media (max-width: 480px) {
  .author-note { flex-direction: column; gap: 14px; }
}

/* ── Footer ── */
footer {
  border-top: 1px solid var(--border);
  padding: 40px 0;
  font-family: var(--sans);
  font-size: 0.85rem;
  color: var(--text-tertiary);
}
.footer-inner {
  max-width: var(--wide-width);
  margin: 0 auto;
  padding: 0 24px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 12px;
}
.footer-inner a { color: var(--text-secondary); }

/* ── Responsive ── */
@media (max-width: 640px) {
  h1 { font-size: 1.8rem; }
  h2 { font-size: 1.4rem; }
  .hero { padding: 48px 0 40px; }
  .nav-links { gap: 16px; }
  .qa-role { min-width: 70px; font-size: 0.65rem; }
}