/* ============================================================
   Shared formatting for lecture / problem-set pages.
   Page-specific diagrams and custom layouts remain local.
   ============================================================ */

body.lecture-page {
  font-family: 'Inter', 'Segoe UI', system-ui, sans-serif;
  padding-top: 70px;
  max-width: 900px;
  margin: auto;
  background-color: #f1f5f9;
  color: #1e293b;
  line-height: 1.7;
}

body.dark-mode.lecture-page {
  background-color: #0f1117;
  color: #e8edf5;
}

body.lecture-page main {
  padding: 24px 20px 40px;
}

body.lecture-page main h1 {
  font-weight: 800;
  color: #18398a;
  font-size: clamp(24px, 2.4vw, 32px);
  margin-bottom: 24px;
  line-height: 1.12;
  letter-spacing: -0.025em;
  padding-left: 18px;
  border-left: 5px solid #18398a;
}

body.dark-mode.lecture-page main h1 {
  color: #90c4f9;
  border-left-color: #60a5fa;
}

/* ── Problem card ────────────────────────────────────────── */
.problem {
  margin-bottom: 36px;
  padding: 24px;
  border: 1px solid #dde6f5;
  border-top: 4px solid #18398a;
  border-radius: 12px;
  background: #ffffff;
  box-shadow: 0 3px 14px rgba(15, 23, 42, 0.09);
  transition: box-shadow 0.22s, transform 0.22s;
}

.problem:hover {
  box-shadow: 0 8px 28px rgba(24, 57, 138, 0.14);
  transform: translateY(-2px);
}

/* Problem heading — clean, no Comic Sans */
.problem h3 {
  background: linear-gradient(90deg, #e8f0ff 0%, #eff6ff 100%);
  color: #1e293b;
  padding: 12px 18px 12px 20px;
  border-left: 5px solid #18398a;
  border-radius: 0 8px 8px 0;
  font-size: 17px;
  font-weight: 700;
  font-family: 'Inter', 'Segoe UI', system-ui, sans-serif;
  line-height: 1.5;
  margin-bottom: 18px;
  margin-top: 0;
  box-shadow: none;
}

/* ── Solution panel ──────────────────────────────────────── */
.solution {
  display: none;
  margin: 20px -24px 0;
  padding: 20px 24px;
  background-color: #f0f4ff;
  border-top: 1px solid #dbe5f5;
  border-left: 4px solid #18398a;
  border-radius: 0 0 12px 12px;
}

/* ── Math box ────────────────────────────────────────────── */
.math-box {
  border: 1px solid #c7d9f5;
  padding: 14px 18px;
  background-color: #f0f4ff;
  border-radius: 8px;
  margin: 12px 0;
  display: block;
  font-size: 17px;
  overflow-x: auto;
  max-width: 100%;
  box-sizing: border-box;
  color: #1e293b;
}

/* ── Note / callout box ──────────────────────────────────── */
.note-box {
  padding: 14px 16px;
  border-radius: 8px;
  margin: 14px 0;
  font-size: 14px;
  line-height: 1.65;
  border-left: 4px solid #f59e0b;
  background-color: #fef9ec;
  color: #78350f;
}

/* ── Body text in lecture pages ──────────────────────────── */
body.lecture-page p,
body.lecture-page ol,
body.lecture-page li {
  font-family: 'Inter', 'Segoe UI', system-ui, sans-serif;
  font-size: 16px;
  line-height: 1.75;
  color: #334155;
  margin-bottom: 12px;
}

body.lecture-page ol {
  padding-left: 24px;
}

/* ── Tables ──────────────────────────────────────────────── */
body.lecture-page table {
  width: 100%;
  border-collapse: collapse;
  margin: 16px 0;
  background: #fff;
  border-radius: 8px;
  overflow: hidden;
  box-shadow: 0 1px 4px rgba(15, 23, 42, 0.06);
}

body.lecture-page th,
body.lecture-page td {
  border: 1px solid #e2e8f0;
  padding: 9px 12px;
  vertical-align: top;
  font-size: 14px;
}

body.lecture-page th {
  background: #eff6ff;
  color: #18398a;
  font-weight: 700;
  font-size: 13px;
  text-transform: uppercase;
  letter-spacing: 0.03em;
}

/* ── Buttons in lecture pages ────────────────────────────── */
body.lecture-page button {
  background-color: #18398a;
  color: #fff;
  border: 0;
  padding: 9px 20px;
  border-radius: 6px;
  cursor: pointer;
  font-size: 15px;
  font-weight: 600;
  font-family: 'Inter', 'Segoe UI', system-ui, sans-serif;
  transition: background-color 0.18s;
}

body.lecture-page button:hover {
  background-color: #0e2a6d;
}

body.lecture-page button:focus-visible {
  outline: 3px solid rgba(37, 99, 235, 0.4);
  outline-offset: 2px;
}

/* ── Dark mode ───────────────────────────────────────────── */
body.dark-mode .problem {
  background-color: #1a1f2e;
  border-color: #2b3650;
  border-top-color: #3b82f6;
  box-shadow: 0 3px 14px rgba(0, 0, 0, 0.28);
}

body.dark-mode .problem:hover {
  box-shadow: 0 8px 28px rgba(0, 0, 0, 0.40);
}

body.dark-mode .problem h3 {
  background: linear-gradient(90deg, #1a2d50 0%, #1e2d4a 100%);
  border-left-color: #60a5fa;
  color: #dbeafe;
}

body.dark-mode .solution {
  background-color: #141c2e;
  border-top-color: #2b3650;
  border-left-color: #60a5fa;
}

body.dark-mode .math-box {
  background-color: #1a2540;
  border-color: #2b4070;
  color: #d1daf0;
}

body.dark-mode .note-box {
  background-color: #2a1f0a;
  border-left-color: #fbbf24;
  color: #fef3c7;
}

body.dark-mode.lecture-page p,
body.dark-mode.lecture-page li,
body.dark-mode.lecture-page ol {
  color: #c8d0df;
}

body.dark-mode.lecture-page table {
  background: #1a1f2e;
}

body.dark-mode.lecture-page th,
body.dark-mode.lecture-page td {
  border-color: #2b3650;
}

body.dark-mode.lecture-page th {
  background: #1e2d4a;
  color: #93c5fd;
}

body.dark-mode.lecture-page button {
  background-color: #1e3a8a;
}

body.dark-mode.lecture-page button:hover {
  background-color: #2548b0;
}

/* ── Responsive ──────────────────────────────────────────── */
@media (max-width: 700px) {
  body.lecture-page {
    max-width: none;
  }

  body.lecture-page main {
    padding: 16px 14px 30px;
  }

  .problem {
    padding: 16px;
  }

  .solution {
    margin-inline: -16px;
    padding-inline: 16px;
  }
}