/* ============================================================
   Pivot Teach — Lesson stylesheet
   Shared by every lesson. Tufte-inspired: serif body, generous
   margins, side notes, restrained color. Prints well.
   ============================================================ */

:root {
  --serif: "Source Serif Pro", "Noto Serif SC", "Songti SC", "STSong", Georgia, serif;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif;
  --mono: "SF Mono", "JetBrains Mono", "Fira Code", Menlo, monospace;

  --ink: #1a1a1a;
  --ink-soft: #555;
  --ink-faint: #888;
  --rule: #d8d4cc;
  --rule-soft: #ece8e0;
  --paper: #fdfcf8;
  --paper-warm: #f6f3eb;

  --accent: #8b2c1f;       /* deep brick red — Pivot brand hint */
  --accent-soft: #f4e8e4;
  --link: #5a4a8a;
  --link-hover: #3d2f6e;

  --max-width: 760px;
  --side-note-width: 200px;
  --with-sides-width: calc(var(--max-width) + var(--side-note-width) * 2);
}

/* ---------- Reset ---------- */
*, *::before, *::after { box-sizing: border-box; }
html { -webkit-font-smoothing: antialiased; -moz-osx-font-smoothing: grayscale; }
body {
  margin: 0;
  font-family: var(--serif);
  font-size: 17px;
  line-height: 1.65;
  color: var(--ink);
  background: var(--paper);
}

/* ---------- Layout ---------- */
.lesson {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 4rem 1.5rem 6rem;
}
@media (min-width: 1180px) {
  body { background: var(--paper-warm); }
  .lesson {
    max-width: var(--with-sides-width);
    padding: 5rem 1.5rem 8rem;
    position: relative;
  }
}

/* ---------- Header ---------- */
.lesson-header {
  border-bottom: 1px solid var(--rule);
  padding-bottom: 1.5rem;
  margin-bottom: 3rem;
}
.lesson-meta {
  font-family: var(--sans);
  font-size: 0.78rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--ink-faint);
  margin-bottom: 0.5rem;
}
.lesson-meta a { color: var(--ink-faint); text-decoration: none; }
.lesson-meta a:hover { color: var(--accent); }
.lesson-title {
  font-size: 2.1rem;
  line-height: 1.2;
  font-weight: 600;
  margin: 0 0 0.6rem;
  letter-spacing: -0.01em;
}
.lesson-subtitle {
  font-size: 1.05rem;
  color: var(--ink-soft);
  font-style: italic;
  margin: 0;
}

/* ---------- Typography ---------- */
h2 {
  font-size: 1.45rem;
  margin: 2.6rem 0 1rem;
  font-weight: 600;
  letter-spacing: -0.005em;
  color: var(--ink);
}
h3 {
  font-size: 1.15rem;
  margin: 2rem 0 0.6rem;
  font-weight: 600;
  color: var(--ink);
}
p { margin: 0 0 1.2rem; }
a { color: var(--link); text-decoration: underline; text-decoration-color: var(--rule); text-underline-offset: 2px; }
a:hover { color: var(--link-hover); text-decoration-color: var(--link-hover); }

strong { font-weight: 600; color: var(--ink); }
em { font-style: italic; }

ul, ol { margin: 0 0 1.2rem; padding-left: 1.6rem; }
li { margin-bottom: 0.4rem; }

code, kbd {
  font-family: var(--mono);
  font-size: 0.88em;
  background: var(--paper-warm);
  padding: 0.1em 0.35em;
  border-radius: 3px;
  color: var(--accent);
}
pre {
  font-family: var(--mono);
  font-size: 0.85rem;
  line-height: 1.55;
  background: #2a2520;
  color: #e8dfd0;
  padding: 1.2rem 1.4rem;
  border-radius: 6px;
  overflow-x: auto;
  margin: 1.4rem 0;
}
pre code { background: none; color: inherit; padding: 0; font-size: inherit; }

blockquote {
  margin: 1.6rem 0;
  padding: 0.2rem 0 0.2rem 1.2rem;
  border-left: 3px solid var(--accent);
  color: var(--ink-soft);
  font-style: italic;
}

hr {
  border: none;
  border-top: 1px solid var(--rule);
  margin: 3rem 0;
}

/* ---------- Side notes (margin notes — Tufte style) ---------- */
@media (min-width: 1180px) {
  .side-note {
    float: right;
    clear: right;
    width: var(--side-note-width);
    margin: 0.3rem -260px 0.6rem 1.2rem;
    font-family: var(--sans);
    font-size: 0.82rem;
    line-height: 1.5;
    color: var(--ink-soft);
  }
  .side-note strong { color: var(--accent); font-weight: 600; }
}
.side-note-inline {
  display: block;
  font-family: var(--sans);
  font-size: 0.82rem;
  color: var(--ink-soft);
  margin: 0.6rem 0 1rem;
  padding: 0.6rem 0.9rem;
  background: var(--paper-warm);
  border-left: 2px solid var(--rule);
  border-radius: 0 3px 3px 0;
}
@media (min-width: 1180px) {
  .side-note-inline { display: none; }
}

/* ---------- Pivot-anchored callouts ---------- */
.pivot-callout {
  background: var(--accent-soft);
  border-left: 3px solid var(--accent);
  padding: 1rem 1.3rem;
  margin: 1.8rem 0;
  border-radius: 0 4px 4px 0;
}
.pivot-callout .label {
  font-family: var(--sans);
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--accent);
  margin-bottom: 0.4rem;
}
.pivot-callout p:last-child { margin-bottom: 0; }

/* ---------- Diagrams ---------- */
.diagram {
  margin: 2rem 0;
  padding: 1.5rem;
  background: #fff;
  border: 1px solid var(--rule);
  border-radius: 6px;
  text-align: center;
}
.diagram svg { max-width: 100%; height: auto; }
.diagram .caption {
  font-family: var(--sans);
  font-size: 0.8rem;
  color: var(--ink-faint);
  margin-top: 0.8rem;
  font-style: italic;
}

/* ---------- Tables ---------- */
table {
  width: 100%;
  border-collapse: collapse;
  margin: 1.5rem 0;
  font-size: 0.92rem;
}
th, td {
  text-align: left;
  padding: 0.7rem 0.9rem;
  border-bottom: 1px solid var(--rule);
  vertical-align: top;
}
th {
  font-family: var(--sans);
  font-size: 0.78rem;
  font-weight: 600;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: var(--ink-soft);
  border-bottom: 2px solid var(--ink);
}
tr:last-child td { border-bottom: none; }

/* ---------- Quiz ---------- */
.quiz {
  margin: 2.5rem 0;
  padding: 1.6rem 1.8rem;
  background: #fff;
  border: 1px solid var(--rule);
  border-radius: 6px;
}
.quiz-title {
  font-family: var(--sans);
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--accent);
  margin-bottom: 0.4rem;
}
.quiz-question {
  font-size: 1.05rem;
  margin-bottom: 1.2rem;
  color: var(--ink);
}
.quiz-options {
  display: flex;
  flex-direction: column;
  gap: 0.6rem;
}
.quiz-option {
  display: block;
  width: 100%;
  text-align: left;
  font-family: var(--serif);
  font-size: 0.98rem;
  padding: 0.75rem 1rem;
  background: var(--paper-warm);
  border: 1px solid var(--rule);
  border-radius: 4px;
  cursor: pointer;
  transition: all 0.15s;
  color: var(--ink);
}
.quiz-option:hover { background: #fff; border-color: var(--ink-soft); }
.quiz-option.correct {
  background: #e8f0e4;
  border-color: #6a8a52;
  color: #2d4520;
}
.quiz-option.wrong {
  background: #f4e4e0;
  border-color: var(--accent);
  color: var(--accent);
}
.quiz-feedback {
  margin-top: 1rem;
  padding: 0.9rem 1rem;
  font-family: var(--sans);
  font-size: 0.9rem;
  line-height: 1.55;
  border-radius: 4px;
  display: none;
}
.quiz-feedback.shown { display: block; }
.quiz-feedback.correct { background: #e8f0e4; color: #2d4520; }
.quiz-feedback.wrong { background: var(--accent-soft); color: var(--accent); }

/* ---------- Footer ---------- */
.lesson-footer {
  margin-top: 3.5rem;
  padding-top: 2rem;
  border-top: 1px solid var(--rule);
}
.primary-source {
  padding: 1.2rem 1.4rem;
  background: var(--paper-warm);
  border-radius: 6px;
  margin-bottom: 1.5rem;
}
.primary-source .label {
  font-family: var(--sans);
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--accent);
  margin-bottom: 0.5rem;
}
.followup {
  font-family: var(--sans);
  font-size: 0.95rem;
  color: var(--ink-soft);
  padding: 1.2rem 1.4rem;
  background: #fff;
  border: 1px dashed var(--rule);
  border-radius: 6px;
  line-height: 1.55;
}
.lesson-nav {
  display: flex;
  justify-content: space-between;
  margin-top: 2rem;
  font-family: var(--sans);
  font-size: 0.88rem;
}
.lesson-nav a { color: var(--ink-soft); text-decoration: none; }
.lesson-nav a:hover { color: var(--accent); }

/* ---------- Print ---------- */
@media print {
  body { background: #fff; font-size: 11pt; }
  .lesson { max-width: none; margin: 0; padding: 1cm; }
  .quiz-option { background: none; border: 1px solid #999; }
  .pivot-callout, .primary-source, .followup { background: none; border: 1px solid #999; }
  a { color: #333; text-decoration: underline; }
  .side-note { display: none; }
}