/* Shared stylesheet for all perfin lessons — Tufte-inspired */

:root {
  --text: #1a1a1a;
  --bg: #fafaf7;
  --surface: #ffffff;
  --accent: #1a5276;
  --accent-light: #d6eaf8;
  --muted: #6c757d;
  --border: #d5d8dc;
  --success: #1e8449;
  --success-bg: #eafaf1;
  --warn: #b7950b;
  --warn-bg: #fef9e7;
  --danger: #922b21;
  --danger-bg: #fdedec;
  --formula-bg: #f0f0f0;
  --mono: 'SFMono-Regular', 'Consolas', monospace;
  --serif: Georgia, 'Times New Roman', serif;
  --sans: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif;
  --max-width: 720px;
}

/* ── Dark mode via OS preference ── */
@media (prefers-color-scheme: dark) {
  :root {
    --text: #e8e6e1;
    --bg: #1a1a1e;
    --surface: #24242a;
    --accent: #5b9bd5;
    --accent-light: #1c2f45;
    --muted: #8a8a99;
    --border: #38383f;
    --success: #4caf7d;
    --success-bg: #0d2a1a;
    --warn: #d4a843;
    --warn-bg: #2a220a;
    --danger: #e05c5c;
    --danger-bg: #2a0f0f;
    --formula-bg: #2a2a30;
  }
}

/* ── Manual dark mode override (toggled by JS) ── */
[data-theme="dark"] {
  --text: #e8e6e1;
  --bg: #1a1a1e;
  --surface: #24242a;
  --accent: #5b9bd5;
  --accent-light: #1c2f45;
  --muted: #8a8a99;
  --border: #38383f;
  --success: #4caf7d;
  --success-bg: #0d2a1a;
  --warn: #d4a843;
  --warn-bg: #2a220a;
  --danger: #e05c5c;
  --danger-bg: #2a0f0f;
  --formula-bg: #2a2a30;
}

[data-theme="light"] {
  --text: #1a1a1a;
  --bg: #fafaf7;
  --surface: #ffffff;
  --accent: #1a5276;
  --accent-light: #d6eaf8;
  --muted: #6c757d;
  --border: #d5d8dc;
  --success: #1e8449;
  --success-bg: #eafaf1;
  --warn: #b7950b;
  --warn-bg: #fef9e7;
  --danger: #922b21;
  --danger-bg: #fdedec;
  --formula-bg: #f0f0f0;
}

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

body {
  font-family: var(--sans);
  font-size: 18px;
  line-height: 1.7;
  color: var(--text);
  background: var(--bg);
  padding: 4rem 1.5rem 5rem;
  transition: background 0.2s, color 0.2s;
}

@media (max-width: 540px) {
  body {
    padding: 4rem 0.75rem 4rem;
    font-size: 16px;
  }
}

.lesson-wrap { max-width: var(--max-width); margin: 0 auto; }

/* ── Theme toggle ── */
.top-bar {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 100;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.6rem 1rem;
  gap: 0.5rem;
  background: var(--bg);
  border-bottom: 1px solid var(--border);
}

.top-bar-right {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  flex-shrink: 0;
}

/* ── Hamburger (mobile only) ── */
.hamburger-wrap {
  display: none;
  position: relative;
}

.hamburger-btn {
  background: var(--surface);
  border: 1.5px solid var(--border);
  border-radius: 999px;
  padding: 0.35rem 0.85rem;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.82rem;
  line-height: 1.5;
}

.hamburger-icon {
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  width: 18px;
  height: 13px;
  background: transparent;
}
.hamburger-icon::before,
.hamburger-icon span,
.hamburger-icon::after {
  content: "";
  display: block;
  width: 18px;
  height: 2px;
  background: var(--muted);
  border-radius: 2px;
  transition: transform 0.2s, opacity 0.2s;
}
.hamburger-icon.open::before { transform: translateY(5.5px) rotate(45deg); }
.hamburger-icon.open span    { opacity: 0; }
.hamburger-icon.open::after  { transform: translateY(-5.5px) rotate(-45deg); }

.hamburger-menu {
  position: absolute;
  top: calc(100% + 0.5rem);
  left: 0;
  background: var(--surface);
  border: 1.5px solid var(--border);
  border-radius: 12px;
  padding: 0.4rem;
  display: flex;
  flex-direction: column;
  gap: 0.25rem;
  min-width: 140px;
  box-shadow: 0 4px 16px rgba(0,0,0,0.15);
  z-index: 200;
}

.hamburger-menu-link {
  display: block;
  padding: 0.5rem 0.85rem;
  font-size: 0.88rem;
  font-weight: 600;
  color: var(--muted);
  text-decoration: none;
  border-radius: 8px;
  transition: background 0.12s, color 0.12s;
}
.hamburger-menu-link:hover { background: var(--bg); color: var(--accent); }

.theme-toggle {
  background: var(--surface);
  border: 1.5px solid var(--border);
  border-radius: 999px;
  padding: 0.35rem 0.85rem;
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--muted);
  cursor: pointer;
  z-index: 100;
  transition: border-color 0.15s, color 0.15s;
  display: flex;
  align-items: center;
  gap: 0.4rem;
}
.theme-toggle:hover { border-color: var(--accent); color: var(--accent); }

.auth-nav {
  display: flex;
  margin: 0;
}
.auth-nav-btn {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  background: var(--surface);
  border: 1.5px solid var(--border);
  border-radius: 999px;
  padding: 0.35rem 0.85rem;
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--muted);
  cursor: pointer;
  text-decoration: none;
  transition: border-color 0.15s, color 0.15s;
}
.auth-nav-btn:hover { border-color: var(--accent); color: var(--accent); }
.auth-nav-btn:visited { color: var(--muted); }

.main-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  min-width: 0;
}
.main-nav-link {
  display: inline-flex;
  align-items: center;
  background: var(--surface);
  border: 1.5px solid var(--border);
  border-radius: 999px;
  padding: 0.35rem 0.85rem;
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--muted);
  text-decoration: none;
  transition: border-color 0.15s, color 0.15s;
}
.main-nav-link:hover { border-color: var(--accent); color: var(--accent); }
.main-nav-link:visited { color: var(--muted); }

@media (max-width: 540px) {
  .main-nav { display: none; }
  .hamburger-wrap { display: block; }
}

/* ── Header ── */
.lesson-header { margin-bottom: 2.5rem; padding-bottom: 1rem; border-bottom: 2px solid var(--accent); }
.lesson-tag { font-size: 0.75rem; font-weight: 700; letter-spacing: 0.08em; text-transform: uppercase; color: var(--muted); }
h1 { font-family: var(--serif); font-size: 2rem; font-weight: 700; line-height: 1.2; margin-top: 0.25rem; }
.lesson-meta { font-size: 0.85rem; color: var(--muted); margin-top: 0.5rem; }
.lesson-meta a { color: var(--accent); }

/* ── Body typography ── */
h2 { font-family: var(--serif); font-size: 1.4rem; margin: 2rem 0 0.6rem; color: var(--accent); }
h3 { font-size: 1.05rem; font-weight: 700; margin: 1.5rem 0 0.4rem; }
p  { margin-bottom: 1rem; }
a  { color: var(--accent); }
a:visited { color: var(--accent); opacity: 0.75; }

ul, ol { margin: 0.5rem 0 1rem 1.5rem; }
li { margin-bottom: 0.35rem; }

/* ── Callout boxes ── */
.callout {
  padding: 1rem 1.25rem;
  border-left: 4px solid var(--accent);
  background: var(--accent-light);
  border-radius: 0 6px 6px 0;
  margin: 1.5rem 0;
}
.callout.warn  { border-color: var(--warn);    background: var(--warn-bg);    }
.callout.tip   { border-color: var(--success); background: var(--success-bg); }
.callout-label { font-size: 0.72rem; font-weight: 700; letter-spacing: 0.07em; text-transform: uppercase; color: var(--muted); display: block; margin-bottom: 0.3rem; }

/* ── Key term ── */
.term {
  font-weight: 700;
  border-bottom: 2px dotted var(--accent);
  cursor: help;
}

/* ── Formula / code block ── */
.formula {
  font-family: var(--mono);
  background: var(--formula-bg);
  color: var(--text);
  padding: 0.8rem 1rem;
  border-radius: 6px;
  font-size: 0.9rem;
  overflow-x: auto;
  margin: 1rem 0;
}

/* ── Quiz ── */
.quiz { margin: 2rem 0; }
.quiz-q { font-weight: 700; margin-bottom: 0.75rem; }
.quiz-options { list-style: none; margin-left: 0; }
.quiz-options li { margin-bottom: 0.5rem; }
.quiz-options label {
  display: block;
  padding: 0.6rem 1rem;
  border: 2px solid var(--border);
  border-radius: 6px;
  cursor: pointer;
  background: var(--surface);
  transition: border-color 0.15s, background 0.15s;
}
.quiz-options label:hover { border-color: var(--accent); background: var(--accent-light); }
.quiz-options input[type="radio"] { margin-right: 0.6rem; }
.quiz-feedback { margin-top: 0.75rem; font-weight: 700; display: none; padding: 0.5rem 1rem; border-radius: 6px; }
.quiz-feedback.correct { color: var(--success); background: var(--success-bg); display: block; }
.quiz-feedback.wrong   { color: var(--danger);  background: var(--danger-bg);  display: block; }
.quiz-btn {
  margin-top: 0.5rem;
  padding: 0.5rem 1.4rem;
  background: var(--accent);
  color: #fff;
  border: none;
  border-radius: 6px;
  font-size: 0.95rem;
  cursor: pointer;
}
.quiz-btn:hover { opacity: 0.85; }

/* ── Progress bar (for multi-section lessons) ── */
.progress-bar { height: 4px; background: var(--border); border-radius: 2px; margin-bottom: 2rem; }
.progress-fill { height: 4px; background: var(--accent); border-radius: 2px; transition: width 0.3s; }

/* ── Footer ── */
.lesson-footer {
  margin-top: 3rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--border);
  font-size: 0.88rem;
  color: var(--muted);
}
.lesson-footer .nav-links { display: flex; gap: 1.5rem; flex-wrap: wrap; }
.lesson-footer a { color: var(--accent); }

/* ── Print (always light) ── */
@media print {
  body { background: #fff; color: #1a1a1a; padding: 0; font-size: 11pt; }
  .quiz-btn, .quiz-feedback, .theme-toggle, .auth-nav, .top-bar, .top-bar-right, .main-nav, .hamburger-wrap { display: none !important; }
  a { color: #1a1a1a; text-decoration: underline; }
}