/* ===== Sticky Nav ===== */
.sticky-nav {
  position: sticky; top: 0; z-index: 100;
  background: var(--bg-canvas);
  border-bottom: 1px solid var(--border);
  padding: 0.8rem 2rem 0;
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
}
.nav-inner {
  max-width: 96rem; margin: 0 auto;
  display: flex; align-items: center; justify-content: space-between;
  height: 48px; gap: 1rem;
}
.nav-brand {
  font-family: Georgia, serif;
  font-size: 1.05rem; font-weight: 400;
  color: var(--text);
  letter-spacing: -0.01em;
  white-space: nowrap;
}
.nav-brand span { color: var(--accent); }
.nav-tabs { display: flex; gap: 2px; }
.nav-tab {
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.78rem; font-weight: 400;
  padding: 0.35rem 0.85rem;
  border: 1px solid transparent; border-radius: 4px;
  background: transparent;
  color: var(--muted);
  cursor: pointer;
  transition: all 140ms ease;
}
.nav-tab:hover { color: var(--text); border-color: var(--border); }
.nav-tab.active {
  color: var(--text);
  border-color: var(--accent);
  background: var(--accent-bg);
}
.nav-right { display: flex; align-items: center; gap: 0.4rem; }
.theme-btn {
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.65rem; font-weight: 400;
  padding: 0.25rem 0.5rem;
  border: 1px solid var(--border);
  border-radius: 4px;
  background: transparent;
  color: var(--muted);
  cursor: pointer;
  transition: all 140ms ease;
}
.theme-btn:hover { color: var(--text); border-color: var(--accent); }
.theme-btn.active { color: var(--accent); border-color: var(--accent); background: var(--accent-bg); }

/* ===== Page Shell ===== */
.page-shell {
  max-width: 96rem; margin: 0 auto;
  padding: 1.5rem 2rem 4rem;
}

/* ===== Chapter Nav ===== */
.chapter-nav {
  display: flex; flex-wrap: wrap; gap: 4px;
  margin-bottom: 1.25rem;
  padding-bottom: 1rem;
  border-bottom: 1px solid var(--border);
}
.ch-btn {
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.72rem; font-weight: 400;
  padding: 0.35rem 0.75rem;
  border: 1px solid var(--border);
  border-radius: 4px;
  background: transparent;
  color: var(--muted);
  cursor: pointer;
  transition: all 140ms ease;
  white-space: nowrap;
}
.ch-btn:hover { color: var(--text); border-color: var(--accent); }
.ch-btn.active {
  color: var(--text);
  border-color: var(--accent);
  background: var(--accent-bg);
}

/* ===== Knowledge Card ===== */
.k-card {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: clamp(0.85rem, 1.4vw, 1.15rem) 1.25rem;
  margin-bottom: 0.85rem;
  transition: border-color 200ms cubic-bezier(0.22, 1, 0.36, 1);
}
.k-card:hover { border-color: var(--border-strong); }
.k-card h3 {
  font-size: clamp(1.3rem, 2.6vw, 1.5rem);
  letter-spacing: -0.015em;
  margin-bottom: 0.85rem;
  padding-bottom: 0.65rem;
  border-bottom: 1px solid var(--border);
}
.k-card h4 {
  font-size: 1rem;
  color: var(--accent);
  margin: 1rem 0 0.45rem;
  font-weight: 400;
}
.k-card p {
  font-size: 0.96rem; line-height: 1.55;
  margin-bottom: 0.45rem;
}
.k-card ul {
  padding-left: 1.15rem; margin-bottom: 0.45rem;
}
.k-card li {
  font-size: 0.96rem; line-height: 1.55;
  margin-bottom: 0.25rem;
}
.k-card li::marker { color: var(--accent); }

/* Highlight box */
.hl {
  background: var(--accent-bg);
  border-left: 2px solid var(--accent);
  border-radius: 0 4px 4px 0;
  padding: 0.65rem 0.9rem;
  margin: 0.65rem 0;
  font-size: 0.92rem; line-height: 1.55;
}
.hl strong { color: var(--text); font-weight: 450; }

/* Table */
.k-table {
  width: 100%; border-collapse: collapse;
  margin: 0.65rem 0; font-size: 0.82rem;
  border-radius: 4px; overflow: hidden;
}
.k-table th {
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.72rem; font-weight: 400;
  background: var(--panel-soft);
  color: var(--accent);
  padding: 0.5rem 0.65rem;
  text-align: left;
  border: 1px solid var(--border);
  text-transform: uppercase;
  letter-spacing: 0.04em;
}
.k-table td {
  padding: 0.5rem 0.65rem;
  border: 1px solid var(--border);
  vertical-align: top;
}
.k-table tr:nth-child(even) td { background: var(--panel-soft); }

/* Section Label — accent left-border pill */
.section-label {
  display: inline-flex; align-items: center;
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.65rem; font-weight: 400;
  padding: 0.15rem 0.55rem;
  border: 1px solid var(--border);
  border-left: 2px solid var(--accent);
  border-radius: 999px;
  color: var(--muted-strong);
  margin-bottom: 0.65rem;
  background: transparent;
}

/* ===== Calc Tutorial ===== */
.calc-box {
  background: var(--panel-soft);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: clamp(0.85rem, 1.4vw, 1.15rem) 1.15rem;
  margin: 0.65rem 0;
}
.calc-box .calc-title {
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.82rem; font-weight: 400;
  color: var(--accent);
  margin-bottom: 0.65rem;
  display: flex; align-items: center; gap: 0.4rem;
}
.calc-step {
  display: flex; gap: 0.65rem; align-items: flex-start;
  margin-bottom: 0.5rem; font-size: 0.92rem; line-height: 1.55;
}
.calc-step .step-num {
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.65rem; font-weight: 400;
  color: var(--accent);
  min-width: 1.35rem; height: 1.35rem;
  display: flex; align-items: center; justify-content: center;
  border: 1px solid var(--accent);
  border-radius: 50%;
  flex-shrink: 0; margin-top: 0.1rem;
}
.calc-formula {
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.82rem;
  background: var(--bg-canvas);
  border: 1px solid var(--border);
  border-radius: 4px;
  padding: 0.55rem 0.9rem;
  margin: 0.5rem 0;
  color: var(--text);
  overflow-x: auto;
  line-height: 1.45;
}
.calc-note {
  font-size: 0.78rem; color: var(--muted);
  font-style: italic; margin-top: 0.35rem;
}

/* ===== SVG Diagram ===== */
.diagram-wrap {
  background: var(--panel-soft);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 0.85rem;
  margin: 0.65rem 0;
  text-align: center;
  overflow-x: auto;
}
.diagram-wrap svg { max-width: 100%; height: auto; }
.diagram-caption {
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.65rem; color: var(--muted);
  margin-top: 0.4rem;
}

/* ===== Bracket Buttons — Pi.dev style [text] ===== */
.btn-bracket {
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.78rem; font-weight: 400;
  padding: 0.4rem 0.95rem;
  border: 1px solid var(--border);
  border-radius: 4px;
  background: transparent;
  color: var(--muted-strong);
  cursor: pointer;
  transition: all 140ms ease;
}
.btn-bracket:hover { border-color: var(--accent); color: var(--text); }
.btn-bracket.primary { color: var(--accent); border-color: var(--accent); }
.btn-bracket.primary:hover { background: var(--accent-bg); }
.btn-bracket:disabled { opacity: 0.3; cursor: not-allowed; }