/* ---------------------------------------------------------
   Reset
--------------------------------------------------------- */
*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body { margin: 0; }
img { max-width: 100%; height: auto; display: block; }
a { color: inherit; }
table { border-collapse: collapse; }

/* ---------------------------------------------------------
   Design tokens
--------------------------------------------------------- */
:root {
  --color-bg: #ffffff;
  --color-bg-subtle: #f7f7fb;
  --color-border: #e3e3ef;
  --color-text: #191932;
  --color-text-muted: #5f5f78;
  --color-tint: #eef0ff;
  --color-tint-border: #d9ddff;
  --color-accent: #4338ca;
  --color-accent-ink: #35299e;
  --color-accent-tint: #eef0ff;
  --font-sans: "Segoe UI", -apple-system, BlinkMacSystemFont, Roboto, Helvetica, Arial, sans-serif;
  --font-mono: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
  --radius: 12px;
  --container: 860px;
}

body {
  font-family: var(--font-sans);
  color: var(--color-text);
  background: var(--color-bg);
  line-height: 1.65;
  font-size: 17px;
}

.container {
  max-width: var(--container);
  margin: 0 auto;
  padding: 0 24px;
}

h1, h2, h3 {
  font-family: var(--font-sans);
  font-weight: 700;
  line-height: 1.25;
  color: var(--color-text);
}

h1 { font-size: 2rem; margin: 0 0 12px; letter-spacing: -0.01em; }
h2 { font-size: 1.4rem; margin: 46px 0 16px; letter-spacing: -0.005em; }
h3 { font-size: 1.05rem; margin: 0 0 4px; }

p { margin: 0 0 16px; color: var(--color-text); }
ul, ol { margin: 0 0 16px; padding-left: 22px; }
li { margin-bottom: 6px; }

.lede {
  font-size: 1.1rem;
  color: var(--color-text-muted);
}

/* ---------------------------------------------------------
   Header / Footer (identical markup on all 4 pages)
--------------------------------------------------------- */
.site-header {
  border-bottom: 1px solid var(--color-border);
}

.site-header .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 68px;
}

.site-logo {
  display: flex;
  align-items: center;
  gap: 8px;
  text-decoration: none;
  color: var(--color-text);
  font-weight: 700;
  font-size: 1.05rem;
}

.site-logo__mark {
  width: 26px;
  height: 26px;
  border-radius: 7px;
  background: var(--color-accent);
  color: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
  flex: 0 0 auto;
}

.site-nav {
  display: flex;
  gap: 26px;
  list-style: none;
  margin: 0;
  padding: 0;
}

.site-nav a {
  text-decoration: none;
  color: var(--color-text-muted);
  font-size: 0.95rem;
}

.site-nav a:hover,
.site-nav a[aria-current="page"] {
  color: var(--color-accent-ink);
}

.site-footer {
  margin-top: 64px;
  border-top: 1px solid var(--color-border);
}

.footer-cta {
  background: var(--color-bg-subtle);
  padding: 24px 0;
}

.footer-cta p {
  margin: 0;
  font-size: 0.95rem;
  color: var(--color-text-muted);
}

.footer-cta a {
  color: var(--color-accent-ink);
  text-decoration: underline;
}

.footer-bottom {
  padding: 20px 0 32px;
}

.footer-bottom .container {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
}

.site-footer nav {
  display: flex;
  gap: 20px;
  flex-wrap: wrap;
}

.site-footer nav a {
  text-decoration: none;
  color: var(--color-text-muted);
  font-size: 0.9rem;
}

.site-footer nav a:hover { color: var(--color-text); }

.footer-note {
  font-size: 0.85rem;
  color: var(--color-text-muted);
  max-width: 640px;
  margin: 16px 0 0;
}

/* ---------------------------------------------------------
   Hero band + breadcrumbs
--------------------------------------------------------- */
.hero-band {
  background: var(--color-tint);
  padding-bottom: 32px;
}

.breadcrumbs {
  font-size: 0.85rem;
  color: var(--color-text-muted);
  margin: 0;
  padding: 22px 0 18px;
  list-style: none;
  display: flex;
  gap: 6px;
}
.breadcrumbs a { color: var(--color-text-muted); text-decoration: none; }
.breadcrumbs a:hover { text-decoration: underline; }
.breadcrumbs li:not(:last-child)::after { content: "/"; margin-left: 6px; color: var(--color-tint-border); }

/* ---------------------------------------------------------
   Article shell
--------------------------------------------------------- */
main { padding-bottom: 24px; }

.article-header {
  padding: 8px 0 0;
}

.hero-band > .container > .article-header:first-child {
  padding-top: 22px;
}

.article-meta {
  display: flex;
  align-items: center;
  gap: 16px;
  flex-wrap: wrap;
  font-size: 0.85rem;
  color: var(--color-text-muted);
  margin: 4px 0 16px;
}

.author-avatar {
  width: 30px;
  height: 30px;
  border-radius: 50%;
  background: var(--color-accent);
  color: #fff;
  font-size: 0.75rem;
  font-weight: 700;
  display: flex;
  align-items: center;
  justify-content: center;
  flex: 0 0 auto;
}

/* ---------------------------------------------------------
   Kicker badge + centered article header (home page)
--------------------------------------------------------- */
.kicker-badge {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  background: #ffffff;
  border: 1px solid var(--color-tint-border);
  border-radius: 999px;
  padding: 7px 16px;
  font-size: 0.8rem;
  font-weight: 700;
  color: var(--color-accent-ink);
  margin-bottom: 16px;
}

.kicker-badge__dot {
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background: var(--color-accent);
}

.article-header--centered {
  text-align: center;
  max-width: 720px;
  margin: 0 auto;
}

.article-header--centered .article-meta {
  justify-content: center;
}

.article-header--centered .lede {
  max-width: 620px;
  margin: 0 auto;
}

/* ---------------------------------------------------------
   Article images
--------------------------------------------------------- */
.article-figure {
  margin: 28px 0 32px;
}

.hero-figure {
  margin: 28px 0 0;
}

.article-figure img {
  border-radius: var(--radius);
  border: 1px solid var(--color-border);
}

.article-figure figcaption {
  margin-top: 10px;
  font-size: 0.85rem;
  color: var(--color-text-muted);
  text-align: center;
}

/* ---------------------------------------------------------
   Formula callout
--------------------------------------------------------- */
.formula-box {
  border: 1px solid var(--color-tint-border);
  background: var(--color-tint);
  border-radius: var(--radius);
  padding: 20px 24px;
  margin: 20px 0 24px;
  text-align: center;
}

.formula-box code {
  font-family: var(--font-mono);
  font-size: 1.15rem;
  color: var(--color-accent-ink);
  font-weight: 700;
}

.formula-box p {
  margin: 10px 0 0;
  font-size: 0.88rem;
  color: var(--color-text-muted);
}

/* ---------------------------------------------------------
   Diagnostic list
--------------------------------------------------------- */
.diagnostic-list {
  list-style: none;
  margin: 0 0 24px;
  padding: 0;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  overflow: hidden;
}

.diagnostic-list li {
  display: flex;
  gap: 14px;
  padding: 14px 18px;
  margin: 0;
  font-size: 0.95rem;
  border-bottom: 1px solid var(--color-border);
}

.diagnostic-list li:last-child { border-bottom: none; }

.diagnostic-list .num {
  flex: 0 0 auto;
  width: 24px;
  height: 24px;
  border-radius: 50%;
  background: var(--color-accent-tint);
  color: var(--color-accent-ink);
  font-weight: 700;
  font-size: 0.8rem;
  display: flex;
  align-items: center;
  justify-content: center;
  margin-top: 2px;
}

.diagnostic-list strong { color: var(--color-text); }

/* ---------------------------------------------------------
   Checklist rows
--------------------------------------------------------- */
.checklist {
  margin: 24px 0 32px;
  display: flex;
  flex-direction: column;
  gap: 14px;
}

.check-row {
  display: flex;
  gap: 16px;
  padding: 18px 20px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  background: var(--color-bg);
}

.check-row__icon {
  flex: 0 0 auto;
  width: 32px;
  height: 32px;
  border-radius: 50%;
  background: var(--color-accent);
  display: flex;
  align-items: center;
  justify-content: center;
}

.check-row__icon svg {
  width: 16px;
  height: 16px;
  stroke: #fff;
  fill: none;
  stroke-width: 3;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.check-row__body h3 {
  margin: 0 0 4px;
}

.check-row__body p {
  margin: 0;
  font-size: 0.95rem;
  color: var(--color-text-muted);
}

.check-row__body a {
  color: var(--color-accent-ink);
  text-decoration: underline;
}

/* ---------------------------------------------------------
   Tables
--------------------------------------------------------- */
.table-wrap {
  overflow-x: auto;
  margin: 20px 0 28px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
}

table.data-table {
  width: 100%;
  min-width: 480px;
  font-size: 0.92rem;
}

.data-table th,
.data-table td {
  text-align: left;
  padding: 12px 16px;
  border-bottom: 1px solid var(--color-border);
}

.data-table thead th {
  background: var(--color-bg-subtle);
  font-weight: 700;
  color: var(--color-text-muted);
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.03em;
}

.data-table tbody tr:last-child td { border-bottom: none; }

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

/* ---------------------------------------------------------
   FAQ
--------------------------------------------------------- */
.faq-item {
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 4px 20px;
  margin-bottom: 12px;
  background: var(--color-bg);
}

.faq-item summary {
  cursor: pointer;
  font-weight: 700;
  padding: 16px 0;
  list-style: none;
}

.faq-item summary::-webkit-details-marker { display: none; }

.faq-item summary::before {
  content: "+";
  display: inline-block;
  width: 18px;
  color: var(--color-accent-ink);
  font-weight: 700;
}

.faq-item[open] summary::before { content: "\2212"; }

.faq-item p {
  margin: 0 0 16px;
  color: var(--color-text-muted);
}

/* ---------------------------------------------------------
   Misc content blocks
--------------------------------------------------------- */
.notice {
  background: var(--color-bg-subtle);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 16px 20px;
  font-size: 0.9rem;
  color: var(--color-text-muted);
  margin: 20px 0 28px;
}

@media (max-width: 560px) {
  .diagnostic-list li { flex-direction: row; }
  h1 { font-size: 1.6rem; }
}