/* =========================================================
   数式大全 — スタイルシート
   ========================================================= */

:root {
  --bg: #f6f7fb;
  --bg-soft: #ffffff;
  --ink: #1e2433;
  --ink-soft: #5b6472;
  --border: #e6e8ef;
  --accent: #2563eb;
  --accent-soft: #eef2ff;
  --radius-lg: 18px;
  --radius-md: 12px;
  --radius-sm: 8px;
  --shadow-sm: 0 1px 3px rgba(30, 36, 51, 0.06), 0 1px 2px rgba(30, 36, 51, 0.04);
  --shadow-md: 0 8px 24px rgba(30, 36, 51, 0.08);
  --shadow-lg: 0 20px 48px rgba(30, 36, 51, 0.14);
  --header-h: 88px;
  font-size: 16px;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: "Zen Kaku Gothic New", "Noto Sans JP", -apple-system, BlinkMacSystemFont, sans-serif;
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
}

body.modal-lock { overflow: hidden; }

a { color: inherit; }

/* ===================== ヘッダー ===================== */
.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  height: var(--header-h);
  background: linear-gradient(135deg, #101636 0%, #1e2f6e 45%, #2b4bb8 100%);
  box-shadow: 0 4px 20px rgba(16, 22, 54, 0.25);
}

.header-inner {
  max-width: 1440px;
  margin: 0 auto;
  height: 100%;
  padding: 0 28px;
  display: flex;
  align-items: center;
  gap: 20px;
}

.brand { display: flex; align-items: center; gap: 14px; }

.brand-icon {
  width: 52px;
  height: 52px;
  border-radius: 14px;
  background: linear-gradient(135deg, #ffd166, #f9a825);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 24px;
  color: #101636;
  box-shadow: 0 6px 16px rgba(249, 168, 37, 0.4);
  flex-shrink: 0;
}

.brand-text h1 {
  margin: 0;
  font-size: 22px;
  font-weight: 900;
  color: #fff;
  letter-spacing: 0.5px;
  display: flex;
  align-items: baseline;
  gap: 10px;
}

.brand-sub {
  font-size: 10px;
  font-weight: 500;
  color: #9fb2ea;
  letter-spacing: 1.5px;
}

.brand-tagline {
  margin: 2px 0 0;
  font-size: 12.5px;
  color: #c3cef2;
  font-weight: 500;
}

.menu-toggle {
  display: none;
  margin-left: auto;
  background: rgba(255,255,255,0.1);
  border: none;
  color: #fff;
  width: 42px;
  height: 42px;
  border-radius: 10px;
  font-size: 18px;
  cursor: pointer;
}

.header-stats {
  margin-left: auto;
  display: flex;
  gap: 10px;
}

.stat-pill {
  display: flex;
  align-items: center;
  gap: 8px;
  background: rgba(255, 255, 255, 0.1);
  border: 1px solid rgba(255, 255, 255, 0.15);
  color: #e8ecfb;
  padding: 8px 16px;
  border-radius: 999px;
  font-size: 13px;
  font-weight: 600;
  white-space: nowrap;
}

.stat-pill i { color: #ffd166; }

/* ===================== レイアウト ===================== */
.app-shell {
  max-width: 1440px;
  margin: 0 auto;
  display: grid;
  grid-template-columns: 300px 1fr;
  gap: 28px;
  padding: 28px;
  align-items: start;
}

/* ===================== サイドバー ===================== */
.sidebar {
  position: sticky;
  top: calc(var(--header-h) + 20px);
  background: var(--bg-soft);
  border-radius: var(--radius-lg);
  border: 1px solid var(--border);
  box-shadow: var(--shadow-sm);
  padding: 22px 20px;
  max-height: calc(100vh - var(--header-h) - 40px);
  overflow-y: auto;
  display: flex;
  flex-direction: column;
  gap: 22px;
}

.sidebar-section { display: flex; flex-direction: column; gap: 10px; }

.sidebar-label {
  font-size: 13px;
  font-weight: 700;
  color: var(--ink-soft);
  display: flex;
  align-items: center;
  gap: 6px;
}

.sidebar-label-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.mini-link {
  background: none;
  border: none;
  color: var(--accent);
  font-size: 12px;
  font-weight: 700;
  cursor: pointer;
  padding: 2px 4px;
}
.mini-link:hover { text-decoration: underline; }

.search-box {
  position: relative;
  display: flex;
  align-items: center;
}

.search-box input {
  width: 100%;
  padding: 11px 36px 11px 14px;
  border-radius: var(--radius-md);
  border: 1.5px solid var(--border);
  font-size: 14px;
  font-family: inherit;
  outline: none;
  transition: border-color 0.15s;
  background: #fbfcfe;
}
.search-box input:focus { border-color: var(--accent); background: #fff; }

.search-clear {
  position: absolute;
  right: 8px;
  background: none;
  border: none;
  color: #9aa4b5;
  cursor: pointer;
  font-size: 13px;
  opacity: 0;
  pointer-events: none;
  padding: 6px;
}
.search-clear.show { opacity: 1; pointer-events: auto; }
.search-clear:hover { color: #e11d48; }

.chip-list { display: flex; flex-direction: column; gap: 6px; }

.chip {
  --chip-color: #2563eb;
  display: flex;
  align-items: center;
  gap: 9px;
  background: #fbfcfe;
  border: 1.5px solid var(--border);
  border-radius: 10px;
  padding: 9px 12px;
  font-size: 13.5px;
  font-weight: 600;
  color: var(--ink);
  cursor: pointer;
  text-align: left;
  transition: all 0.15s;
}
.chip i { color: var(--chip-color); width: 16px; text-align: center; }
.chip span:first-of-type { flex: 1; }
.chip-count {
  background: #eef1f6;
  color: #7a8496;
  font-size: 11px;
  font-weight: 700;
  padding: 2px 7px;
  border-radius: 999px;
}
.chip:hover { border-color: var(--chip-color); transform: translateX(2px); }
.chip.active {
  background: var(--chip-color);
  border-color: var(--chip-color);
  color: #fff;
}
.chip.active i { color: #fff; }
.chip.active .chip-count { background: rgba(255,255,255,0.25); color: #fff; }

.freq-filter { display: flex; flex-direction: column; gap: 6px; }
.freq-btn {
  display: flex;
  align-items: center;
  gap: 8px;
  border: 1.5px solid var(--border);
  background: #fbfcfe;
  border-radius: 10px;
  padding: 8px 12px;
  font-size: 13px;
  font-weight: 700;
  color: var(--ink);
  cursor: pointer;
}
.freq-hint { font-size: 11px; font-weight: 500; color: var(--ink-soft); }
.freq-btn:hover { border-color: #f9a825; }
.freq-btn.active { background: #fff7e6; border-color: #f9a825; color: #b45309; }

.level-filter { display: flex; flex-wrap: wrap; gap: 8px; }
.level-btn {
  --level-color: #2563eb;
  --level-bg: #eff6ff;
  border: 1.5px solid var(--border);
  background: #fbfcfe;
  border-radius: 999px;
  padding: 7px 13px;
  font-size: 12.5px;
  font-weight: 700;
  color: var(--ink-soft);
  cursor: pointer;
}
.level-btn:hover { border-color: var(--level-color); }
.level-btn.active {
  background: var(--level-bg);
  border-color: var(--level-color);
  color: var(--level-color);
}

.sidebar-footer-note {
  font-size: 12px;
  color: var(--ink-soft);
  line-height: 1.6;
  background: #fffbeb;
  border: 1px solid #fde68a;
  border-radius: var(--radius-md);
  padding: 12px 14px;
  display: flex;
  gap: 8px;
}
.sidebar-footer-note i { color: #d97706; margin-top: 2px; }

.sidebar-backdrop {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(15, 20, 40, 0.5);
  z-index: 60;
}
.sidebar-backdrop.show { display: block; }

/* ===================== メインコンテンツ ===================== */
.main-content { min-width: 0; }

.hero {
  background: linear-gradient(135deg, #eef2ff 0%, #f5f8ff 60%, #fdf6ec 100%);
  border: 1px solid #e3e8fb;
  border-radius: var(--radius-lg);
  padding: 32px 36px;
  margin-bottom: 22px;
}
.hero h2 {
  margin: 0 0 10px;
  font-size: 26px;
  font-weight: 900;
  color: #1a2140;
  letter-spacing: 0.3px;
}
.hero p {
  margin: 0 0 20px;
  color: #4b5468;
  font-size: 14.5px;
  line-height: 1.8;
  max-width: 820px;
}
.hero-actions { display: flex; gap: 10px; flex-wrap: wrap; }
.hero-btn {
  display: flex;
  align-items: center;
  gap: 8px;
  border: 1.5px solid #d7ddf5;
  background: #ffffffcc;
  color: #33395a;
  padding: 10px 18px;
  border-radius: 999px;
  font-size: 13.5px;
  font-weight: 700;
  cursor: pointer;
  transition: all 0.15s;
}
.hero-btn:hover { border-color: var(--accent); color: var(--accent); }
.hero-btn.active { background: #1e2f6e; border-color: #1e2f6e; color: #fff; }

/* ---------- ツールバー ---------- */
.toolbar {
  display: flex;
  align-items: center;
  gap: 14px;
  flex-wrap: wrap;
  margin-bottom: 16px;
}
.result-count {
  font-weight: 800;
  font-size: 15px;
  color: #1a2140;
  white-space: nowrap;
}
.active-filters {
  flex: 1;
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
}
.active-tag {
  --tag-color: #2563eb;
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: color-mix(in srgb, var(--tag-color) 12%, white);
  color: var(--tag-color);
  border: 1px solid color-mix(in srgb, var(--tag-color) 35%, white);
  padding: 5px 10px;
  border-radius: 999px;
  font-size: 12px;
  font-weight: 700;
  cursor: pointer;
}
.active-tag i { font-size: 10px; }

.sort-box { display: flex; align-items: center; gap: 8px; color: var(--ink-soft); }
.sort-box select {
  border: 1.5px solid var(--border);
  border-radius: 999px;
  padding: 8px 14px;
  font-size: 13px;
  font-weight: 600;
  color: var(--ink);
  background: #fff;
  cursor: pointer;
  outline: none;
}

/* ===================== カードグリッド ===================== */
.formula-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: 18px;
  padding-bottom: 40px;
}

.formula-card {
  --cat-color: #2563eb;
  background: #fff;
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 20px 20px 16px;
  box-shadow: var(--shadow-sm);
  cursor: pointer;
  transition: transform 0.18s ease, box-shadow 0.18s ease, border-color 0.18s;
  display: flex;
  flex-direction: column;
  gap: 10px;
  position: relative;
  overflow: hidden;
}
.formula-card::before {
  content: "";
  position: absolute;
  top: 0; left: 0;
  width: 100%;
  height: 4px;
  background: var(--cat-color);
}
.formula-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-md);
  border-color: var(--cat-color);
}

.card-top {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
}

.cat-badge {
  --cat-color: inherit;
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-size: 11.5px;
  font-weight: 700;
  color: var(--cat-color);
  background: color-mix(in srgb, var(--cat-color) 10%, white);
  padding: 4px 10px;
  border-radius: 999px;
}
.formula-card .cat-badge { color: var(--cat-color); background: color-mix(in srgb, var(--cat-color) 10%, white); }

.level-badge {
  --lv-color: #2563eb;
  --lv-bg: #eff6ff;
  font-size: 11px;
  font-weight: 800;
  color: var(--lv-color);
  background: var(--lv-bg);
  padding: 4px 10px;
  border-radius: 999px;
  white-space: nowrap;
}

.card-title {
  margin: 0;
  font-size: 16.5px;
  font-weight: 800;
  color: #1a2140;
  line-height: 1.4;
}
.card-title mark, .card-desc mark {
  background: #fff3b0;
  color: inherit;
  border-radius: 3px;
  padding: 0 2px;
}

.card-formula {
  background: #f8f9fd;
  border-radius: var(--radius-md);
  padding: 14px 10px;
  overflow-x: auto;
  font-size: 15px;
  min-height: 52px;
  display: flex;
  align-items: center;
  justify-content: center;
}
.card-formula .katex-display { margin: 0; }

.card-extra-hint {
  font-size: 11.5px;
  color: var(--ink-soft);
  font-weight: 700;
  display: flex;
  align-items: center;
  gap: 5px;
  margin-top: -6px;
}

.card-desc {
  margin: 0;
  font-size: 13px;
  color: var(--ink-soft);
  line-height: 1.65;
  flex: 1;
}

.card-bottom {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding-top: 6px;
  border-top: 1px dashed var(--border);
}

.freq-stars { font-size: 11px; letter-spacing: 2px; color: #dbe0ea; }
.freq-stars .on { color: #f9a825; }

.card-more {
  font-size: 12px;
  font-weight: 700;
  color: var(--cat-color);
  display: flex;
  align-items: center;
  gap: 5px;
}

/* ===================== 検索結果なし ===================== */
.no-result {
  text-align: center;
  padding: 70px 20px;
  color: var(--ink-soft);
}
.no-result.hidden { display: none; }
.no-result i { font-size: 40px; color: #cbd3e1; margin-bottom: 14px; }

/* ===================== モーダル ===================== */
.modal-backdrop {
  position: fixed;
  inset: 0;
  background: rgba(15, 20, 40, 0.55);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 200;
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.2s;
  padding: 20px;
}
.modal-backdrop.open { opacity: 1; pointer-events: auto; }

.modal-card {
  background: #fff;
  border-radius: 22px;
  max-width: 680px;
  width: 100%;
  max-height: 86vh;
  overflow-y: auto;
  padding: 34px 34px 30px;
  position: relative;
  box-shadow: var(--shadow-lg);
  transform: translateY(16px) scale(0.98);
  transition: transform 0.22s ease;
}
.modal-backdrop.open .modal-card { transform: translateY(0) scale(1); }

.modal-close {
  position: absolute;
  top: 18px;
  right: 18px;
  width: 36px;
  height: 36px;
  border-radius: 50%;
  border: none;
  background: #f1f3f8;
  color: #667;
  font-size: 15px;
  cursor: pointer;
}
.modal-close:hover { background: #e6e9f2; }

.modal-header {
  --cat-color: #2563eb;
  display: flex;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
  margin-bottom: 14px;
}
.modal-header .cat-badge { color: var(--cat-color); background: color-mix(in srgb, var(--cat-color) 10%, white); }
.modal-stars { font-size: 13px; letter-spacing: 2px; }

.modal-title {
  margin: 0 0 18px;
  font-size: 24px;
  font-weight: 900;
  color: #151a30;
  line-height: 1.4;
}

.modal-formula-block {
  background: #f8f9fd;
  border-radius: var(--radius-md);
  padding: 20px 16px;
  margin-bottom: 20px;
  overflow-x: auto;
}
.modal-formula { font-size: 17px; padding: 4px 0; }
.modal-formula .katex-display { margin: 6px 0; }
.modal-alt-label {
  font-size: 12px;
  font-weight: 700;
  color: var(--ink-soft);
  margin: 10px 0 4px;
  border-top: 1px dashed var(--border);
  padding-top: 10px;
}

.modal-desc {
  font-size: 14.5px;
  line-height: 1.9;
  color: #333c4e;
  margin: 0 0 16px;
}

.modal-note {
  display: flex;
  gap: 10px;
  background: #fffbeb;
  border: 1px solid #fde68a;
  border-radius: var(--radius-md);
  padding: 14px 16px;
  font-size: 13px;
  line-height: 1.75;
  color: #78500a;
  margin-bottom: 16px;
}
.modal-note i { color: #d97706; margin-top: 2px; }

.modal-tags { display: flex; flex-wrap: wrap; gap: 6px; }
.tag-pill {
  font-size: 11.5px;
  font-weight: 600;
  color: #566;
  background: #f1f3f8;
  padding: 4px 10px;
  border-radius: 999px;
}

/* ===================== フッター ===================== */
.site-footer {
  text-align: center;
  padding: 26px 20px 40px;
  font-size: 12.5px;
  color: #9aa4b5;
}

/* ===================== トップへ戻る ===================== */
.back-to-top {
  position: fixed;
  right: 26px;
  bottom: 26px;
  width: 46px;
  height: 46px;
  border-radius: 50%;
  background: #1e2f6e;
  color: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: var(--shadow-md);
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.2s, transform 0.2s;
  z-index: 40;
  text-decoration: none;
}
.back-to-top.show { opacity: 1; pointer-events: auto; }
.back-to-top:hover { transform: translateY(-3px); }

/* ===================== レスポンシブ ===================== */
@media (max-width: 980px) {
  .app-shell {
    grid-template-columns: 1fr;
    padding: 18px;
  }
  .menu-toggle { display: flex; align-items: center; justify-content: center; }
  .header-stats { display: none; }

  .sidebar {
    position: fixed;
    top: 0;
    left: 0;
    height: 100vh;
    max-height: 100vh;
    width: 300px;
    z-index: 70;
    transform: translateX(-110%);
    transition: transform 0.25s ease;
    border-radius: 0;
  }
  .sidebar.open { transform: translateX(0); }
}

@media (max-width: 640px) {
  .header-inner { padding: 0 16px; }
  .brand-text h1 { font-size: 18px; }
  .brand-tagline { display: none; }
  .brand-icon { width: 42px; height: 42px; font-size: 19px; }

  .hero { padding: 24px 20px; }
  .hero h2 { font-size: 20px; }

  .formula-grid { grid-template-columns: 1fr; }
  .toolbar { flex-direction: column; align-items: stretch; }
  .sort-box { justify-content: space-between; }
  .sort-box select { flex: 1; }

  .modal-card { padding: 26px 20px 22px; max-height: 92vh; }
  .modal-title { font-size: 20px; }
}