/* POM Tutorials - INSEAD-inspired theme */
:root {
  --navy: #003346;
  --teal: #007a5e;
  --teal-light: #00a37a;
  --white: #ffffff;
  --off-white: #f7f8fa;
  --gray-50: #f9fafb;
  --gray-100: #f3f4f6;
  --gray-200: #e5e7eb;
  --gray-300: #d1d5db;
  --gray-500: #6b7280;
  --gray-700: #374151;
  --gray-900: #111827;
  --red-500: #ef4444;
  --amber-100: #fef3c7;
  --amber-700: #b45309;
  --radius: 12px;
  --shadow: 0 1px 3px rgba(0,0,0,.08), 0 1px 2px rgba(0,0,0,.06);
  --shadow-md: 0 4px 6px rgba(0,0,0,.07), 0 2px 4px rgba(0,0,0,.06);
  --shadow-lg: 0 10px 15px rgba(0,0,0,.08), 0 4px 6px rgba(0,0,0,.05);
}

*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html, body { overflow-x: hidden; }

/* ─── Auth Gate (site-wide) ─── */
.auth-gate {
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 100vh;
  background: linear-gradient(135deg, var(--navy) 0%, #004d5a 60%, var(--teal) 100%);
  padding: 1.5rem;
}

.gate-card {
  background: var(--white);
  border-radius: 16px;
  padding: 3rem 2.5rem;
  max-width: 420px;
  width: 100%;
  text-align: center;
  box-shadow: 0 20px 60px rgba(0,0,0,.25);
}

.gate-logo {
  font-size: 1.5rem;
  font-weight: 800;
  color: var(--navy);
  margin-bottom: 1.5rem;
}

.gate-logo span { color: var(--teal); }

.gate-card h1 {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--navy);
  margin-bottom: .35rem;
}

.gate-card > p {
  font-size: .9rem;
  color: var(--gray-500);
  margin-bottom: 2rem;
}

.gate-form {
  display: flex;
  gap: .5rem;
}

.gate-form input {
  flex: 1;
  padding: .7rem 1rem;
  border: 1.5px solid var(--gray-300);
  border-radius: 8px;
  font-size: .95rem;
  outline: none;
  transition: border-color .15s;
}

.gate-form input:focus { border-color: var(--teal); }

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  color: var(--gray-900);
  background: var(--off-white);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

/* ─── Navigation ─── */
.navbar {
  position: sticky;
  top: 0;
  z-index: 100;
  background: var(--navy);
  box-shadow: 0 2px 8px rgba(0,0,0,.15);
}

.nav-inner {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 1.5rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 64px;
}

.nav-brand {
  color: var(--white);
  font-size: 1.15rem;
  font-weight: 700;
  text-decoration: none;
  letter-spacing: .01em;
}

.nav-brand span { color: var(--teal-light); }

.nav-links {
  list-style: none;
  display: flex;
  gap: .25rem;
}

.nav-links a {
  color: rgba(255,255,255,.8);
  text-decoration: none;
  font-size: .875rem;
  font-weight: 500;
  padding: .5rem .85rem;
  border-radius: 6px;
  transition: background .15s, color .15s;
}

.nav-links a:hover,
.nav-links a.active {
  background: rgba(255,255,255,.12);
  color: var(--white);
}

.nav-toggle {
  display: none;
  background: none;
  border: none;
  color: var(--white);
  font-size: 1.5rem;
  cursor: pointer;
  padding: .25rem;
}

/* ─── Hero ─── */
.hero {
  background: linear-gradient(135deg, var(--navy) 0%, #004d5a 100%);
  color: var(--white);
  padding: 3.5rem 1.5rem 3rem;
  text-align: center;
}

.hero h1 {
  font-size: 2.25rem;
  font-weight: 800;
  margin-bottom: .5rem;
}

.hero p {
  font-size: 1.1rem;
  opacity: .85;
  max-width: 600px;
  margin: 0 auto;
}

/* ─── Container ─── */
.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 2rem 1.5rem 4rem;
}

/* ─── Session Cards Grid ─── */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: 1.5rem;
  margin-top: .5rem;
}

.card {
  background: var(--white);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  overflow: hidden;
  transition: transform .2s, box-shadow .2s;
  text-decoration: none;
  color: inherit;
  display: flex;
  flex-direction: column;
}

a.card:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow-lg);
}

.card-header {
  background: var(--navy);
  color: var(--white);
  padding: 1.25rem 1.5rem;
  display: flex;
  align-items: center;
  gap: 1rem;
}

.card-number {
  width: 44px;
  height: 44px;
  background: rgba(255,255,255,.15);
  border-radius: 10px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.25rem;
  font-weight: 800;
  flex-shrink: 0;
}

.card-header-text h3 {
  font-size: 1rem;
  font-weight: 700;
  line-height: 1.3;
}

.card-header-text .card-topic {
  font-size: .8rem;
  opacity: .75;
  margin-top: .15rem;
}

.card-body {
  padding: 1.25rem 1.5rem;
  flex: 1;
}

.card-body p {
  font-size: .9rem;
  color: var(--gray-700);
}

.card-footer {
  padding: .75rem 1.5rem;
  border-top: 1px solid var(--gray-100);
  display: flex;
  align-items: center;
  gap: .5rem;
}

.badge {
  display: inline-flex;
  align-items: center;
  gap: .35rem;
  font-size: .75rem;
  font-weight: 600;
  padding: .3rem .7rem;
  border-radius: 999px;
}

.badge-available {
  background: #dcfce7;
  color: #166534;
}

.badge-coming {
  background: var(--amber-100);
  color: var(--amber-700);
}

/* ─── Session Page ─── */
.session-hero {
  background: linear-gradient(135deg, var(--navy) 0%, #004d5a 100%);
  color: var(--white);
  padding: 2.5rem 1.5rem 2rem;
  overflow: hidden;
  word-wrap: break-word;
}

.session-hero .container {
  padding-top: 0;
  padding-bottom: 0;
}

.breadcrumb {
  font-size: .85rem;
  opacity: .7;
  margin-bottom: .75rem;
}

.breadcrumb a {
  color: var(--white);
  text-decoration: none;
}

.breadcrumb a:hover { text-decoration: underline; }

.session-hero h1 {
  font-size: 2rem;
  font-weight: 800;
}

.session-hero .subtitle {
  font-size: 1rem;
  opacity: .8;
  margin-top: .35rem;
}

.session-content {
  max-width: 900px;
  margin: 0 auto;
  padding: 2rem 1.5rem 4rem;
}

.section {
  margin-bottom: 2.5rem;
}

.section h2 {
  font-size: 1.35rem;
  font-weight: 700;
  color: var(--navy);
  margin-bottom: 1rem;
  padding-bottom: .5rem;
  border-bottom: 2px solid var(--gray-200);
}

/* ─── Present Slides Button ─── */
.present-btn {
  display: inline-flex;
  align-items: center;
  gap: .5rem;
  padding: .65rem 1.5rem;
  background: var(--navy);
  color: var(--white);
  border-radius: 8px;
  font-weight: 600;
  font-size: .95rem;
  text-decoration: none;
  margin-bottom: 1.25rem;
  transition: background .15s, transform .1s;
}

.present-btn:hover {
  background: #004d5a;
  transform: translateY(-1px);
}

/* ─── Materials List ─── */
.materials-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: .75rem;
}

.materials-list li a {
  display: flex;
  align-items: center;
  gap: .85rem;
  padding: 1rem 1.25rem;
  background: var(--white);
  border: 1px solid var(--gray-200);
  border-radius: 10px;
  text-decoration: none;
  color: var(--gray-900);
  font-weight: 500;
  font-size: .95rem;
  transition: border-color .15s, box-shadow .15s;
}

.materials-list li a:hover {
  border-color: var(--teal);
  box-shadow: var(--shadow-md);
}

.file-icon {
  width: 40px;
  height: 40px;
  background: #fee2e2;
  color: #dc2626;
  border-radius: 8px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: .7rem;
  font-weight: 800;
  flex-shrink: 0;
}

/* ─── Recording Video Player ─── */
.recording-section {
  margin: 1rem 0 1.5rem;
}
.recording-toggle {
  display: flex;
  align-items: center;
  gap: .75rem;
  width: 100%;
  padding: 1rem 1.5rem;
  background: linear-gradient(135deg, #eff6ff, #dbeafe);
  border: 2px solid #3b82f6;
  border-radius: 12px;
  cursor: pointer;
  font-size: 1rem;
  transition: all .2s;
}
.recording-toggle:hover {
  background: linear-gradient(135deg, #dbeafe, #bfdbfe);
  box-shadow: 0 4px 12px rgba(59, 130, 246, .2);
}
.recording-toggle .toggle-icon {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  background: #3b82f6;
  color: #fff;
  border-radius: 8px;
  font-size: 1rem;
  flex-shrink: 0;
}
.recording-toggle span:nth-child(2) {
  font-weight: 700;
  color: #1e40af;
  font-size: 1.05rem;
}
.recording-badge {
  font-size: .65rem;
  font-weight: 700;
  text-transform: uppercase;
  background: #3b82f6;
  color: #fff;
  padding: .2rem .6rem;
  border-radius: 4px;
  letter-spacing: .05em;
}
.recording-player {
  margin-top: .75rem;
  border-radius: 12px;
  overflow: hidden;
  background: #000;
  box-shadow: 0 4px 20px rgba(0,0,0,.15);
}
.recording-player video {
  display: block;
  width: 100%;
  border-radius: 12px;
}
.recording-player.hidden {
  display: none;
}

.recording-loading {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: .75rem;
  padding: 2rem;
  color: #64748b;
  font-size: .95rem;
}
.recording-loading.hidden { display: none; }
.loading-spinner {
  width: 24px; height: 24px;
  border: 3px solid #e2e8f0;
  border-top-color: #3b82f6;
  border-radius: 50%;
  animation: spin .8s linear infinite;
}
@keyframes spin { to { transform: rotate(360deg); } }

/* ─── Problems List ─── */
.problems-list {
  list-style: none;
  counter-reset: problem;
}

.problems-list li {
  counter-increment: problem;
  padding: .85rem 1rem .85rem 1rem;
  background: var(--white);
  border: 1px solid var(--gray-200);
  border-radius: 8px;
  margin-bottom: .6rem;
  font-size: .925rem;
  display: flex;
  align-items: flex-start;
  gap: .75rem;
}

.problem-num {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 28px;
  height: 28px;
  background: var(--navy);
  color: var(--white);
  border-radius: 6px;
  font-size: .75rem;
  font-weight: 700;
  flex-shrink: 0;
}

.problem-detail {
  flex: 1;
}

.problem-detail strong {
  color: var(--navy);
}

.difficulty {
  font-size: .75rem;
  color: var(--gray-500);
  margin-left: .25rem;
}

.sub-questions {
  list-style: lower-alpha;
  margin-top: .35rem;
  padding-left: 1.25rem;
  font-size: .85rem;
  color: var(--gray-700);
}

.sub-questions li {
  background: none;
  border: none;
  padding: .15rem 0;
  margin-bottom: 0;
  display: list-item;
}

/* ─── Buttons ─── */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: .6rem 1.25rem;
  font-size: .9rem;
  font-weight: 600;
  border: none;
  border-radius: 8px;
  cursor: pointer;
  transition: background .15s;
}

.btn-primary {
  background: var(--teal);
  color: var(--white);
}

.btn-primary:hover {
  background: var(--teal-light);
}

.password-error {
  color: var(--red-500);
  font-size: .825rem;
  margin-top: .5rem;
  min-height: 1.2em;
}

/* ─── Problem Blocks with Inline Solutions ─── */
.problem-block {
  background: var(--white);
  border: 1px solid var(--gray-200);
  border-radius: 10px;
  margin-bottom: 1.25rem;
  overflow: hidden;
}

.problem-header {
  display: flex;
  align-items: center;
  gap: .75rem;
  padding: 1rem 1.25rem;
  background: var(--gray-50);
  border-bottom: 1px solid var(--gray-200);
}

.problem-part {
  padding: .85rem 1.25rem;
  border-bottom: 1px solid var(--gray-100);
}

.problem-part:last-child {
  border-bottom: none;
}

.part-question {
  display: flex;
  align-items: flex-start;
  gap: .5rem;
  font-size: .9rem;
  color: var(--gray-900);
  margin-bottom: .5rem;
}

.part-letter {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 24px;
  height: 24px;
  background: var(--navy);
  color: var(--white);
  border-radius: 5px;
  font-size: .7rem;
  font-weight: 700;
  flex-shrink: 0;
}

.solution-toggle {
  display: inline-flex;
  align-items: center;
  gap: .5rem;
  background: none;
  border: 1px solid var(--teal);
  color: var(--teal);
  border-radius: 6px;
  padding: .35rem .85rem;
  font-size: .8rem;
  font-weight: 600;
  cursor: pointer;
  transition: background .15s, color .15s;
  margin-bottom: .25rem;
}

.solution-toggle:hover {
  background: var(--teal);
  color: var(--white);
}

.solution-toggle .chevron {
  transition: transform .2s;
  font-size: .65rem;
}

.solution-toggle[aria-expanded="true"] .chevron {
  transform: rotate(90deg);
}

.solution-body {
  display: none;
  padding: 1.25rem 1.5rem;
  margin-top: .5rem;
  font-size: .875rem;
  line-height: 1.75;
  color: var(--gray-700);
  background: #f0fdf4;
  border: 1px solid #bbf7d0;
  border-radius: 8px;
}

.solution-body.open {
  display: block;
}

.solution-body strong {
  color: var(--navy);
}

.solution-body em {
  color: var(--gray-500);
  font-style: italic;
}

.solution-body h4 {
  font-size: .95rem;
  color: var(--navy);
  margin: 1.25rem 0 .5rem 0;
  padding-bottom: .3rem;
  border-bottom: 1px solid #bbf7d0;
}

.solution-body h4:first-of-type {
  margin-top: .75rem;
}

.solution-body p {
  margin: .5rem 0;
}

.solution-body ul, .solution-body ol {
  margin: .5rem 0 .5rem 1.25rem;
}

.solution-body li {
  margin-bottom: .3rem;
}

.solution-body table {
  border-collapse: collapse;
  width: 100%;
  margin: .5rem 0;
  font-size: .85rem;
  display: block;
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
}

.problem-context table {
  border-collapse: collapse;
  width: 100%;
  margin: .5rem 0;
  font-size: .85rem;
  display: block;
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
}

.solution-answer {
  background: #dcfce7;
  border: 1px solid #86efac;
  border-radius: 8px;
  padding: .75rem 1rem;
  font-size: 1rem;
  font-weight: 600;
  color: #166534;
}

.solution-tip {
  background: #eff6ff;
  border: 1px solid #bfdbfe;
  border-left: 3px solid #3b82f6;
  border-radius: 6px;
  padding: .75rem 1rem;
  margin-top: 1rem;
  font-size: .85rem;
  color: #1e40af;
  line-height: 1.6;
}

.problem-context {
  padding: .75rem 1.25rem;
  margin-bottom: 1rem;
  font-size: .875rem;
  line-height: 1.7;
  color: var(--gray-700);
  background: var(--gray-50);
  border: 1px solid var(--gray-200);
  border-radius: 8px;
}

/* ─── Further Reading ─── */
.reading-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: .6rem;
}

.reading-list li a {
  display: flex;
  align-items: center;
  gap: .65rem;
  padding: .75rem 1rem;
  background: var(--white);
  border: 1px solid var(--gray-200);
  border-radius: 8px;
  text-decoration: none;
  color: var(--teal);
  font-weight: 500;
  font-size: .9rem;
  transition: border-color .15s;
}

.reading-list li a:hover {
  border-color: var(--teal);
}

.link-arrow {
  margin-left: auto;
  opacity: .4;
}

/* ─── Key Concepts Grid ─── */
.concepts-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 1rem;
}

.concept-card {
  background: var(--white);
  border: 1px solid var(--gray-200);
  border-radius: 10px;
  padding: 1.15rem 1.25rem;
  transition: box-shadow .15s;
}

.concept-card:hover {
  box-shadow: var(--shadow-md);
}

.concept-icon {
  font-size: 1.5rem;
  margin-bottom: .35rem;
}

.concept-card h4 {
  font-size: .95rem;
  font-weight: 700;
  color: var(--navy);
  margin-bottom: .35rem;
}

.concept-card p {
  font-size: .85rem;
  color: var(--gray-700);
  line-height: 1.55;
}

/* ─── Hints (collapsible) ─── */
.hints-list {
  display: flex;
  flex-direction: column;
  gap: .5rem;
}

.hint-toggle {
  width: 100%;
  text-align: left;
  background: var(--gray-50);
  border: 1px solid var(--gray-200);
  border-radius: 8px;
  padding: .75rem 1rem;
  font-size: .9rem;
  font-weight: 600;
  color: var(--navy);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: space-between;
  transition: background .15s;
}

.hint-toggle:hover {
  background: var(--gray-100);
}

.hint-toggle .chevron {
  transition: transform .2s;
  font-size: .75rem;
}

.hint-toggle[aria-expanded="true"] .chevron {
  transform: rotate(90deg);
}

.hint-body {
  display: none;
  padding: .75rem 1rem;
  font-size: .875rem;
  color: var(--gray-700);
  line-height: 1.6;
  background: #f0fdf4;
  border: 1px solid #bbf7d0;
  border-radius: 0 0 8px 8px;
  margin-top: -1px;
}

.hint-body.open {
  display: block;
}

/* ─── Diagrams ─── */
.diagram-block {
  background: var(--white);
  border: 1px solid var(--gray-200);
  border-radius: 10px;
  padding: 1.25rem;
  margin-bottom: 1rem;
  overflow-x: auto;
}

.diagram-block h4 {
  font-size: .9rem;
  font-weight: 600;
  color: var(--navy);
  margin-bottom: .75rem;
}

.diagram-block svg {
  display: block;
  margin: 0 auto;
}

/* ─── Coming Soon Page ─── */
.coming-soon {
  text-align: center;
  padding: 4rem 1.5rem;
}

.coming-soon .icon {
  font-size: 3.5rem;
  margin-bottom: 1rem;
}

.coming-soon h2 {
  border: none;
  font-size: 1.5rem;
  padding-bottom: 0;
}

.coming-soon p {
  color: var(--gray-500);
  margin-top: .5rem;
}

/* ─── Footer ─── */
.footer {
  text-align: center;
  padding: 1.5rem;
  font-size: .8rem;
  color: var(--gray-500);
  border-top: 1px solid var(--gray-200);
  background: var(--white);
}

.formula-box .katex { font-size: 1.2em; }

/* ─── Responsive ─── */
@media (max-width: 768px) {
  .nav-toggle { display: block; }
  .nav-links {
    display: none;
    position: absolute;
    top: 64px;
    left: 0;
    right: 0;
    background: var(--navy);
    flex-direction: column;
    padding: .5rem 1rem 1rem;
    box-shadow: 0 4px 12px rgba(0,0,0,.2);
  }
  .nav-links.open { display: flex; }
  .nav-links a { padding: .65rem .85rem; }
  .hero h1 { font-size: 1.65rem; }
  .card-grid { grid-template-columns: 1fr; }
  .session-hero h1 { font-size: 1.35rem; }
  .session-hero .subtitle { font-size: .9rem; }
  .session-hero { padding: 2rem 1rem 1.5rem; }
  .password-row { flex-direction: column; }
}