/* ── Reset & base ── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
:root {
  --ink:       #18181B;
  --ink-2:     #52525B;
  --ink-3:     #A1A1AA;
  --bg:        #FFFFFF;
  --bg-soft:   #FAFAFA;
  --border:    #E4E4E7;
  --accent:    #52525B;
  --accent-bg: #F4F4F5;
  --red-bg:    #FFF1F2;
  --red-text:  #E11D48;
  --red-light: #FFE4E6;
  --blue-bg:   #EFF6FF;
  --blue-text: #1D4ED8;
  --yellow-bg: #FEFCE8;
  --yellow-text:#A16207;
  --sans: system-ui, -apple-system, 'Segoe UI', sans-serif;
  --serif: 'DM Serif Display', Georgia, serif;
  --r: 8px;
  --r-lg: 12px;
  --nav-h: 60px;
  --content: 720px;
  --wide: 1100px;
}
body { font-family: var(--sans); background: var(--bg); color: var(--ink); font-size: 16px; line-height: 1.6; -webkit-font-smoothing: antialiased; }
a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }
img { max-width: 100%; display: block; }

/* ── Nav ── */
.site-nav {
  height: var(--nav-h);
  border-bottom: 1px solid var(--border);
  display: flex;
  align-items: center;
  padding: 0 24px;
  position: sticky;
  top: 0;
  background: rgba(255,255,255,0.95);
  backdrop-filter: blur(8px);
  z-index: 100;
}
.site-nav-inner {
  max-width: var(--wide);
  margin: 0 auto;
  width: 100%;
  display: flex;
  align-items: center;
  gap: 32px;
}
.site-logo {
  font-family: var(--serif);
  font-size: 18px;
  color: var(--ink);
  text-decoration: none;
  flex-shrink: 0;
  letter-spacing: -0.02em;
}
.site-logo:hover { text-decoration: none; color: var(--ink); }
.site-logo em { color: var(--accent); font-style: normal; }
.site-nav-links {
  display: flex;
  align-items: center;
  gap: 24px;
  flex: 1;
}
.site-nav-links a {
  font-size: 14px;
  font-weight: 500;
  color: var(--ink-2);
  text-decoration: none;
  transition: color 0.12s;
}
.site-nav-links a:hover, .site-nav-links a.active { color: var(--ink); text-decoration: none; }
.site-nav-cta {
  margin-left: auto;
  font-size: 13px;
  color: var(--ink-3);
}

/* ── Nav dropdown ── */
.site-nav-dropdown { position: relative; }
.site-nav-dropdown-trigger {
  display: flex; align-items: center;
  font-size: 14px; font-weight: 500;
  color: var(--ink-2); text-decoration: none;
  cursor: pointer; transition: color 0.12s;
  padding: 4px 0;
}
.site-nav-dropdown-trigger:hover,
.site-nav-dropdown-trigger.active { color: var(--ink); text-decoration: none; }
.site-nav-dropdown-menu {
  display: none;
  position: absolute;
  top: calc(100% + 10px);
  left: -12px;
  background: #fff;
  border: 1px solid var(--border);
  border-radius: var(--r-lg);
  box-shadow: 0 8px 24px rgba(0,0,0,0.09);
  min-width: 240px;
  z-index: 200;
  padding: 6px;
  overflow: hidden;
}
.site-nav-dropdown:hover .site-nav-dropdown-menu { display: block; }
.site-nav-dropdown-item {
  display: flex; align-items: center; justify-content: space-between;
  padding: 9px 12px;
  font-size: 13.5px;
  color: var(--ink-2);
  text-decoration: none;
  border-radius: 8px;
  transition: background 0.1s, color 0.1s;
  gap: 12px;
}
.site-nav-dropdown-item:hover { background: var(--bg-soft); color: var(--ink); text-decoration: none; }
.site-nav-dropdown-count {
  font-size: 11px; color: var(--ink-3);
  background: var(--bg-soft);
  padding: 1px 7px; border-radius: 10px;
  flex-shrink: 0;
}

/* ── Page shell ── */
.site-page {
  max-width: var(--wide);
  margin: 0 auto;
  padding: 40px 24px 80px;
}
.site-page-narrow {
  max-width: var(--content);
  margin: 0 auto;
  padding: 40px 24px 80px;
}

/* ── Breadcrumb ── */
.site-breadcrumb {
  display: flex;
  align-items: center;
  gap: 6px;
  font-size: 12.5px;
  color: var(--ink-3);
  margin-bottom: 32px;
  flex-wrap: wrap;
}
.site-breadcrumb a { color: var(--ink-3); text-decoration: none; transition: color 0.12s; }
.site-breadcrumb a:hover { color: var(--ink); }
.site-breadcrumb-sep { opacity: 0.4; }

/* ── Section label ── */
.site-section-label {
  font-size: 11px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--ink-3);
  margin-bottom: 20px;
}

/* ── Hero ── */
.site-hero {
  padding: 64px 24px 56px;
  text-align: center;
  border-bottom: 1px solid var(--border);
  margin-bottom: 48px;
  background: var(--bg-soft);
}
.site-hero h1 {
  font-family: var(--serif);
  font-size: 48px;
  line-height: 1.15;
  letter-spacing: -0.03em;
  color: var(--ink);
  margin-bottom: 16px;
}
.site-hero p {
  font-size: 17px;
  color: var(--ink-2);
  max-width: 520px;
  margin: 0 auto 28px;
  line-height: 1.6;
}
.site-hero-meta {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 24px;
  font-size: 13px;
  color: var(--ink-3);
  flex-wrap: wrap;
}
.site-hero-meta strong { color: var(--ink); font-weight: 600; }

/* ── Category card grid ── */
.site-cat-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 16px;
}
.site-cat-card {
  border: 1px solid var(--border);
  border-radius: var(--r-lg);
  padding: 24px;
  text-decoration: none;
  display: flex;
  flex-direction: column;
  gap: 8px;
  transition: border-color 0.13s, box-shadow 0.13s, transform 0.13s;
  background: var(--bg);
}
.site-cat-card:hover {
  border-color: var(--accent);
  box-shadow: 0 4px 20px rgba(0,0,0,0.06);
  transform: translateY(-2px);
  text-decoration: none;
}
.site-cat-icon {
  width: 40px; height: 40px;
  border-radius: 10px;
  background: var(--accent-bg);
  display: flex; align-items: center; justify-content: center;
  margin-bottom: 4px;
}
.site-cat-icon svg { width: 20px; height: 20px; color: var(--accent); }
.site-cat-title {
  font-family: var(--serif);
  font-size: 17px;
  color: var(--ink);
  line-height: 1.3;
}
.site-cat-count { font-size: 13px; color: var(--ink-3); }
.site-cat-bar { height: 2px; background: var(--border); border-radius: 2px; overflow: hidden; margin-top: auto; padding-top: 12px; }
.site-cat-bar-fill { height: 100%; background: var(--accent); border-radius: 2px; }

/* ── Article card grid ── */
.site-art-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 14px;
}
.site-art-grid-4 {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 14px;
}
.site-art-card {
  border: 1px solid var(--border);
  border-radius: var(--r-lg);
  overflow: hidden;
  text-decoration: none;
  display: flex;
  flex-direction: column;
  transition: border-color 0.13s, box-shadow 0.13s, transform 0.13s;
  background: var(--bg);
}
.site-art-card:hover {
  border-color: var(--accent);
  box-shadow: 0 4px 20px rgba(0,0,0,0.06);
  transform: translateY(-2px);
  text-decoration: none;
}
.site-art-thumb {
  height: 120px;
  background: var(--bg-soft);
  display: flex; align-items: center; justify-content: center;
  overflow: hidden;
}
.site-art-thumb img { width: 100%; height: 100%; object-fit: cover; }
.site-art-body { padding: 14px 16px 16px; flex: 1; display: flex; flex-direction: column; gap: 6px; }
.site-art-title {
  font-family: var(--serif);
  font-size: 15px;
  color: var(--ink);
  line-height: 1.4;
  flex: 1;
}
.site-art-meta { display: flex; align-items: center; gap: 8px; flex-wrap: wrap; margin-top: auto; padding-top: 8px; border-top: 1px solid var(--border); font-size: 11.5px; color: var(--ink-3); }

/* ── Level badge ── */
.level-badge { font-size: 10px; font-weight: 700; padding: 2px 7px; border-radius: 10px; letter-spacing: 0.04em; }
.lb-a1, .lb-a2 { background: #F4F4F5; color: #3F3F46; }
.lb-b1, .lb-b2 { background: #DBEAFE; color: #1E40AF; }
.lb-c1, .lb-c2 { background: #F3E8FF; color: #7E22CE; }

/* ── Page heading ── */
.site-page-title {
  font-family: var(--serif);
  font-size: 36px;
  letter-spacing: -0.02em;
  color: var(--ink);
  margin-bottom: 8px;
  line-height: 1.15;
}
.site-page-desc { font-size: 15px; color: var(--ink-2); margin-bottom: 32px; }
.site-color-bar { height: 3px; width: 48px; background: var(--accent); border-radius: 2px; margin-bottom: 20px; }

/* ── Sub-cat heading ── */
.site-subcat-heading {
  font-size: 11px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--ink-3);
  margin: 32px 0 14px;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--border);
}

/* ── Article page ── */
.site-article { max-width: var(--content); margin: 0 auto; padding: 40px 24px 80px; }
.site-art-hero { margin-bottom: 36px; padding-bottom: 28px; border-bottom: 1px solid var(--border); }
.site-art-badges { display: flex; align-items: center; gap: 8px; flex-wrap: wrap; margin-bottom: 16px; }
.site-art-badge { font-size: 11px; font-weight: 600; padding: 3px 10px; border-radius: 12px; background: var(--accent-bg); color: var(--accent); }
.site-art-h1 { font-family: var(--serif); font-size: 38px; line-height: 1.15; letter-spacing: -0.02em; color: var(--ink); margin-bottom: 14px; }
.site-art-byline { font-size: 13px; color: var(--ink-3); display: flex; align-items: center; gap: 16px; flex-wrap: wrap; }
.site-art-byline svg { width: 13px; height: 13px; }

/* ── Article content ── */
.site-art-section { margin-bottom: 36px; }
.site-art-section h2 { font-family: var(--serif); font-size: 24px; color: var(--ink); margin-bottom: 14px; line-height: 1.2; }
.site-art-section p { font-size: 16px; line-height: 1.75; color: var(--ink-2); margin-bottom: 14px; }
.site-art-section p strong { color: var(--ink); }

/* ── Formula ── */
.site-formula { background: var(--bg-soft); border-left: 3px solid var(--accent); border-radius: 0 var(--r) var(--r) 0; padding: 16px 20px; margin-bottom: 12px; }
.site-formula-label { font-size: 10.5px; font-weight: 700; text-transform: uppercase; letter-spacing: 0.08em; color: var(--accent); margin-bottom: 10px; }
.site-formula-row { display: flex; align-items: center; gap: 8px; flex-wrap: wrap; margin-bottom: 8px; }
.ft { display: inline-block; padding: 2px 12px; font-size: 13px; font-weight: 600; background: transparent; line-height: 1.7; }
.ft-sub  { color: #1E40AF; border: 2px solid #1E40AF; border-radius: 48% 52% 45% 55% / 50% 55% 45% 50%; transform: rotate(1deg); }
.ft-verb { color: #92400E; border: 2px solid #92400E; border-radius: 50% 45% 55% 48% / 60% 50% 50% 45%; transform: rotate(-1.5deg); }
.ft-obj  { color: #444;    border: 2px solid #999;   border-radius: 46% 54% 52% 48% / 55% 48% 52% 45%; transform: rotate(0.8deg); }
.ft-neg  { color: #9F1239; border: 2px solid #9F1239; border-radius: 52% 48% 47% 53% / 48% 52% 48% 52%; transform: rotate(-1deg); }
.ft-end  { color: #3F3F46; border: 2px solid #A1A1AA; border-radius: 50% 48% 52% 46% / 52% 50% 50% 48%; transform: rotate(1.2deg); font-size: 11px; }
.site-formula-eg { font-size: 13.5px; color: var(--ink-2); font-style: italic; margin-top: 8px; padding-top: 8px; border-top: 1px solid var(--border); }
.site-formula-eg em { font-style: normal; font-weight: 600; color: var(--ink); }
.site-formula-eg-words { display: flex; align-items: center; gap: 8px; flex-wrap: wrap; margin-top: 6px; }
.site-formula-eg-sep { color: var(--ink-3); font-size: 12px; }
.site-formula-eg-word { font-size: 13px; font-weight: 700; font-style: italic; }
.ft-sub-color  { color: #1E40AF; }
.ft-verb-color { color: #92400E; }
.ft-obj-color  { color: #444; }
.ft-neg-color  { color: #9F1239; }
.ft-end-color  { color: #3F3F46; }

/* ── Examples ── */
.site-examples { display: flex; flex-direction: column; gap: 16px; }
.site-ex-card { background: var(--bg); border: 1px solid var(--border); border-radius: var(--r-lg); overflow: hidden; display: flex; }
.site-ex-illus { width: 320px; flex-shrink: 0; border-right: 1px solid var(--border); overflow: hidden; position: relative; background: var(--bg-soft); }
.site-ex-illus img { width: 100%; height: 100%; object-fit: cover; display: block; min-height: 200px; }
.site-ex-illus-ph { width: 100%; min-height: 200px; display: flex; flex-direction: column; align-items: center; justify-content: center; gap: 6px; color: var(--ink-3); }
.site-ex-illus-ph svg { width: 32px; height: 32px; opacity: 0.2; }
.site-ex-body { flex: 1; padding: 20px 24px; display: flex; flex-direction: column; justify-content: center; gap: 8px; }
.site-ex-num { font-size: 10px; font-weight: 700; text-transform: uppercase; letter-spacing: 0.1em; color: var(--accent); }
.site-ex-sentence { font-size: 18px; color: var(--ink); line-height: 1.55; }
.site-ex-sentence mark { background: none; color: var(--accent); font-weight: 700; border-bottom: 3px solid var(--accent-bg); padding-bottom: 1px; }
.site-ex-pill { display: inline-block; color: var(--accent); font-weight: 600; border: 2px solid var(--accent); border-radius: 50% 45% 55% 48% / 60% 50% 50% 45%; padding: 1px 9px; transform: rotate(-1deg); background: transparent; line-height: 1.6; }
.site-ex-note { font-size: 12.5px; color: var(--ink-3); font-style: italic; }
@media (max-width: 520px) { .site-ex-card { flex-direction: column; } .site-ex-illus { width: 100%; } }

/* ── Use cases ── */
.site-usecases { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; }
.site-uc { border: 1px solid var(--border); border-top: 3px solid var(--accent); border-radius: var(--r); padding: 16px; }
.site-uc-title { font-size: 13.5px; font-weight: 600; color: var(--ink); margin-bottom: 6px; }
.site-uc-desc  { font-size: 13px; color: var(--ink-2); line-height: 1.5; margin-bottom: 8px; }
.site-uc-eg    { font-size: 12px; color: var(--ink-3); font-style: italic; border-top: 1px solid var(--border); padding-top: 8px; }
.site-uc-eg em { font-style: normal; font-weight: 600; color: var(--ink); }

/* ── Signal words ── */
.site-signals { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 12px; }
.site-signal { padding: 6px 16px; background: var(--bg-soft); border: 1px solid var(--border); border-radius: 20px; font-family: var(--serif); font-size: 14px; color: var(--ink); }

/* ── Mistakes ── */
.site-mistakes { display: flex; flex-direction: column; gap: 12px; }
.site-mistake { border-radius: var(--r-lg); overflow: hidden; border: 1px solid var(--border); background: var(--bg); }
.site-mistake-panels { display: flex; }
.site-mx-wrong-panel { flex: 1; padding: 16px 20px; border-right: 1px solid var(--border); display: flex; gap: 12px; align-items: flex-start; }
.site-mx-right-panel { flex: 1; padding: 16px 20px; display: flex; gap: 12px; align-items: flex-start; }
.site-mx-badge { width: 28px; height: 28px; border-radius: 50%; display: flex; align-items: center; justify-content: center; font-size: 12px; font-weight: 800; flex-shrink: 0; margin-top: 2px; }
.site-mx-badge-x  { background: #D97706; color: #fff; }
.site-mx-badge-ok { background: #4338CA; color: #fff; }
.site-mx-label { font-size: 10px; font-weight: 700; text-transform: uppercase; letter-spacing: 0.09em; margin-bottom: 4px; }
.site-mx-label-wrong { color: #D97706; }
.site-mx-label-right { color: #4338CA; }
.site-mx-text-wrong { font-size: 15px; color: var(--ink); line-height: 1.5; }
.site-mx-text-right { font-size: 15px; color: var(--ink); font-weight: 500; line-height: 1.5; }
.site-mx-pill-wrong { display: inline-block; color: #D97706; font-weight: 600; border: 2px solid #D97706; border-radius: 50% 45% 55% 48% / 60% 50% 50% 45%; padding: 1px 9px; transform: rotate(-1.5deg); background: transparent; line-height: 1.6; }
.site-mx-pill-right { display: inline-block; color: #4338CA; font-weight: 600; border: 2px solid #4338CA; border-radius: 48% 52% 45% 55% / 50% 55% 45% 50%; padding: 1px 9px; transform: rotate(1deg); background: transparent; line-height: 1.6; }
.site-mx-note { padding: 10px 20px; font-size: 12.5px; color: var(--ink-2); border-top: 1px solid var(--border); }
.site-mx-note strong { color: var(--ink); }
@media (max-width: 520px) { .site-mistake-panels { flex-direction: column; } .site-mx-wrong-panel { border-right: none; border-bottom: 1px solid var(--border); } }

/* ── Prev/next nav ── */
.site-art-nav { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; margin-top: 48px; padding-top: 28px; border-top: 1px solid var(--border); }
.site-art-nav-card { padding: 16px 20px; border: 1px solid var(--border); border-radius: var(--r-lg); text-decoration: none; display: block; transition: border-color 0.13s; }
.site-art-nav-card:hover { border-color: var(--accent); text-decoration: none; }
.site-art-nav-dir { font-size: 11px; font-weight: 600; text-transform: uppercase; letter-spacing: 0.06em; color: var(--ink-3); margin-bottom: 6px; }
.site-art-nav-title { font-family: var(--serif); font-size: 14.5px; color: var(--ink); line-height: 1.4; }
.site-art-nav-next { text-align: right; }

/* ── Static pages (About, Privacy, etc.) ── */
.site-prose h1 { font-family: var(--serif); font-size: 38px; letter-spacing: -0.02em; margin-bottom: 8px; line-height: 1.15; }
.site-prose h2 { font-family: var(--serif); font-size: 22px; margin: 36px 0 14px; }
.site-prose p  { font-size: 16px; line-height: 1.75; color: var(--ink-2); margin-bottom: 14px; }
.site-prose ul, .site-prose ol { padding-left: 24px; margin-bottom: 14px; }
.site-prose li { font-size: 16px; line-height: 1.75; color: var(--ink-2); margin-bottom: 6px; }
.site-prose a  { color: var(--accent); }
.site-prose .lead { font-size: 18px; color: var(--ink-2); margin-bottom: 36px; padding-bottom: 28px; border-bottom: 1px solid var(--border); }

/* ── Footer ── */
.site-footer {
  border-top: 1px solid var(--border);
  padding: 32px 24px;
  font-size: 13px;
  color: var(--ink-3);
  background: var(--bg-soft);
}
.site-footer-inner {
  max-width: var(--wide);
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 12px;
}
.site-footer-links { display: flex; gap: 20px; flex-wrap: wrap; }
.site-footer-links a { color: var(--ink-3); text-decoration: none; transition: color 0.12s; }
.site-footer-links a:hover { color: var(--ink); }

/* ── Pagination ── */
.site-pagination { display: flex; align-items: center; justify-content: center; gap: 6px; padding: 40px 0; }
.site-page-btn { min-width: 36px; height: 36px; display: flex; align-items: center; justify-content: center; border: 1px solid var(--border); border-radius: var(--r); font-size: 13px; font-weight: 500; color: var(--ink-2); text-decoration: none; transition: all 0.13s; padding: 0 10px; }
.site-page-btn:hover { border-color: var(--accent); color: var(--accent); text-decoration: none; }
.site-page-btn.active { background: var(--accent); border-color: var(--accent); color: #fff; }
.site-page-btn.disabled { opacity: 0.35; pointer-events: none; }
.site-page-dots { color: var(--ink-3); font-size: 13px; padding: 0 4px; }

/* ── Responsive ── */
@media (max-width: 900px) {
  .site-cat-grid { grid-template-columns: repeat(2, 1fr); }
  .site-art-grid { grid-template-columns: repeat(2, 1fr); }
  .site-art-grid-4 { grid-template-columns: repeat(2, 1fr); }
  .site-hero h1 { font-size: 36px; }
  .site-art-h1 { font-size: 28px; }
  .site-usecases { grid-template-columns: 1fr; }
  .site-art-nav { grid-template-columns: 1fr; }
}
@media (max-width: 600px) {
  .site-cat-grid { grid-template-columns: 1fr; }
  .site-art-grid { grid-template-columns: 1fr; }
  .site-art-grid-4 { grid-template-columns: repeat(2, 1fr); }
  .site-page { padding: 24px 16px 60px; }
  .site-article { padding: 24px 16px 60px; }
  .site-hero { padding: 40px 16px 36px; }
  .site-hero h1 { font-size: 28px; }
}