:root {
  --green-950: #0f2f22;
  --green-900: #164232;
  --green-800: #1f5a43;
  --green-700: #2f7a5a;
  --green-600: #43a06f;
  --green-500: #67ba8d;
  --green-100: #e8f6ee;
  --green-050: #f5fbf7;
  --white: #ffffff;
  --text: #21322b;
  --muted: #5d7268;
  --border: #d7e9de;
  --shadow: 0 12px 35px rgba(16, 56, 40, 0.08);
  --radius: 20px;
  --max-width: 1180px;
}

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

html {
  scroll-behavior: smooth;
}

body {
  font-family: Arial, Helvetica, sans-serif;
  color: var(--text);
  background: linear-gradient(180deg, var(--green-050) 0%, #ffffff 35%, #ffffff 100%);
  line-height: 1.6;
}

img {
  max-width: 100%;
  display: block;
}

a {
  text-decoration: none;
  color: inherit;
}

.container {
  width: min(92%, var(--max-width));
  margin: 0 auto;
}

/* Header */
.site-header {
  position: sticky;
  top: 0;
  z-index: 1000;
  background: rgba(255, 255, 255, 0.92);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--border);
}

.nav-container {
  min-height: 78px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
}

.logo {
  font-size: 1.45rem;
  font-weight: 800;
  color: var(--green-950);
  letter-spacing: 0.2px;
}

.logo span {
  color: var(--green-600);
}

.main-nav {
  display: flex;
  gap: 0.6rem;
  flex-wrap: wrap;
}

.main-nav a {
  padding: 0.65rem 1rem;
  border-radius: 999px;
  color: var(--green-800);
  font-weight: 700;
  transition: 0.25s ease;
}

.main-nav a:hover,
.main-nav a.active {
  background: var(--green-100);
  color: var(--green-950);
}

/* Hero */
.hero {
  padding: 5rem 0 4rem;
}

.hero-grid {
  display: grid;
  grid-template-columns: 1.3fr 0.9fr;
  gap: 2rem;
  align-items: center;
}

.badge {
  display: inline-block;
  padding: 0.45rem 0.95rem;
  border-radius: 999px;
  background: var(--green-100);
  color: var(--green-800);
  font-size: 0.95rem;
  font-weight: 700;
  margin-bottom: 1rem;
}

.hero-text h1,
.page-banner h1 {
  color: var(--green-950);
  line-height: 1.15;
}

.hero-text h1 {
  font-size: clamp(2.2rem, 4vw, 3.7rem);
  margin-bottom: 1rem;
}

.hero-text p,
.page-banner p {
  color: var(--muted);
  font-size: 1.08rem;
}

.hero-text p {
  max-width: 58ch;
  margin-bottom: 1.7rem;
}

.hero-actions {
  display: flex;
  gap: 1rem;
  flex-wrap: wrap;
}

.btn {
  display: inline-block;
  padding: 0.95rem 1.35rem;
  border-radius: 14px;
  font-weight: 700;
  transition: 0.25s ease;
}

.btn-primary {
  background: var(--green-700);
  color: var(--white);
  box-shadow: var(--shadow);
}

.btn-primary:hover {
  background: var(--green-800);
  transform: translateY(-2px);
}

.btn-secondary {
  background: var(--white);
  color: var(--green-800);
  border: 1px solid var(--border);
}

.btn-secondary:hover {
  background: var(--green-100);
  transform: translateY(-2px);
}

.hero-panel {
  background: var(--white);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 2rem;
  box-shadow: var(--shadow);
}

.hero-panel h2 {
  color: var(--green-950);
  margin-bottom: 1rem;
  font-size: 1.45rem;
}

.check-list {
  list-style: none;
}

.check-list li {
  padding: 0.75rem 0;
  border-bottom: 1px solid var(--border);
  font-weight: 600;
  color: var(--green-800);
}

.check-list li:last-child {
  border-bottom: none;
}

/* Generic sections */
.section {
  padding: 4rem 0;
}

.alt-section {
  background: linear-gradient(180deg, #ffffff 0%, var(--green-050) 100%);
}

.section-heading {
  text-align: center;
  margin-bottom: 2rem;
}

.section-heading h2 {
  font-size: 2rem;
  color: var(--green-950);
  margin-bottom: 0.5rem;
}

.section-heading p {
  color: var(--muted);
  max-width: 60ch;
  margin: 0 auto;
}

.page-banner {
  padding: 4rem 0 2rem;
}

.page-banner h1 {
  font-size: clamp(2rem, 3vw, 3rem);
  margin: 0.7rem 0;
}

.page-banner p {
  max-width: 55ch;
}

/* Cards */
.card-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 1.4rem;
}

.lecon-card-grid {
  grid-template-columns: repeat(3, 1fr);
}

.lecon-card-grid .card {
  display: flex;
  flex-direction: column;
}

.lecon-card-grid .card .lecon-card-link {
  margin-top: auto;
  align-self: flex-start;
}

.card {
  background: var(--white);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.6rem;
  box-shadow: var(--shadow);
  transition: 0.25s ease;
}

.card:hover {
  transform: translateY(-5px);
}

.card h3 {
  color: var(--green-950);
  margin-bottom: 0.7rem;
  font-size: 1.2rem;
}

.card p {
  color: var(--muted);
  margin-bottom: 1rem;
}

.theme-card {
  background: var(--white);
  border: 2px solid var(--border);
  border-radius: var(--radius);
  padding: 1.6rem;
  box-shadow: var(--shadow);
  transition: 0.25s ease;
  cursor: pointer;
  text-align: center;
  font-weight: 600;
  color: var(--green-950);
  user-select: none;
}

.theme-card:hover {
  transform: translateY(-5px);
  border-color: var(--green-600, #16a34a);
}

.theme-card.selected {
  border-color: var(--green-600, #16a34a);
  background: var(--green-100);
  box-shadow: 0 0 0 3px color-mix(in srgb, var(--green-600, #16a34a) 25%, transparent);
  position: relative;
}

.theme-divider {
  display: flex;
  align-items: center;
  gap: 1rem;
  margin: 2.5rem 0 1.5rem;
}

.theme-divider-line {
  flex: 1;
  height: 2px;
  background: linear-gradient(to right, transparent, var(--green-600, #16a34a), transparent);
  opacity: 0.4;
}

.theme-divider-label {
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--green-950);
  letter-spacing: 0.03em;
  white-space: nowrap;
  padding: 0.3rem 0.9rem;
  border: 1.5px solid var(--green-600, #16a34a);
  border-radius: 999px;
  background: var(--green-100);
  opacity: 0.75;
  transition: opacity 0.3s ease;
}

.theme-divider-label:not(:empty) {
  opacity: 1;
}

.theme-card.selected::after {
  content: '✓';
  position: absolute;
  top: 0.4rem;
  right: 0.6rem;
  font-size: 0.85rem;
  color: var(--green-600, #16a34a);
  font-weight: 700;
}

.icon-circle {
  width: 54px;
  height: 54px;
  border-radius: 16px;
  background: var(--green-100);
  display: grid;
  place-items: center;
  font-size: 1.4rem;
  margin-bottom: 1rem;
}

.text-link {
  color: var(--green-700);
  font-weight: 700;
}

.text-link:hover {
  color: var(--green-900);
}

/* Info boxes */
.info-grid,
.stats-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1.4rem;
}

.info-box,
.stat-box {
  background: var(--white);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.6rem;
  box-shadow: var(--shadow);
}

.info-box h3,
.stat-box h3 {
  color: var(--green-950);
  margin-bottom: 0.7rem;
}

.info-box p,
.stat-box p {
  color: var(--muted);
}

/* Two columns */
.two-columns {
  display: grid;
  grid-template-columns: 1.2fr 0.8fr;
  gap: 1.5rem;
}

.content-box {
  background: var(--white);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.8rem;
  box-shadow: var(--shadow);
}

.content-box h2 {
  color: var(--green-950);
  margin-bottom: 1rem;
  font-size: 1.5rem;
}

.content-box p {
  color: var(--muted);
  margin-bottom: 0.9rem;
}

.content-box p:last-child {
  margin-bottom: 0;
}

.large-box {
  max-width: 900px;
  margin: 0 auto;
}

/* Lists */
.simple-list {
  padding-left: 1.2rem;
  color: var(--muted);
}

.simple-list li {
  margin-bottom: 0.6rem;
}

/* Exercises */
.exercise-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1.4rem;
}

.exercise-card {
  background: var(--white);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.6rem;
  box-shadow: var(--shadow);
  transition: 0.25s ease;
}

.exercise-card:hover {
  transform: translateY(-5px);
}

.exercise-card h3 {
  color: var(--green-950);
  margin: 0.8rem 0 0.7rem;
}

.exercise-card p {
  color: var(--muted);
  margin-bottom: 1rem;
}

.selector-grid {
  margin-bottom: 1.5rem;
}

.subtheme-card.selected {
  border-color: var(--green-700);
  background: #eef8f2;
}

/* Subtheme selector dropdown */
.subtheme-selector-wrapper {
  margin: 2rem 0;
  max-width: 400px;
  margin-left: auto;
  margin-right: auto;
}

.subtheme-select {
  width: 100%;
  padding: 0.95rem 1.2rem;
  border: 2px solid var(--border);
  border-radius: 14px;
  background: var(--white);
  color: var(--text);
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: 0.25s ease;
  appearance: none;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='24' height='24' viewBox='0 0 24 24' fill='none' stroke='%23164232' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpolyline points='6 9 12 15 18 9'%3E%3C/polyline%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 0.8rem center;
  background-size: 1.2em;
  padding-right: 2.5rem;
}

.subtheme-select:hover {
  border-color: var(--green-600);
  box-shadow: 0 4px 12px rgba(16, 56, 40, 0.08);
}

.subtheme-select:focus {
  outline: none;
  border-color: var(--green-600);
  box-shadow: 0 0 0 3px rgba(67, 160, 111, 0.1);
}

.subtheme-select:disabled {
  background-color: #f5f5f5;
  color: var(--muted);
  cursor: not-allowed;
  opacity: 0.6;
}

.subtheme-select option {
  background: var(--white);
  color: var(--text);
  padding: 0.5rem;
}

.helper-text {
  color: var(--muted);
  text-align: center;
  margin: 0.5rem auto 0;
  max-width: 70ch;
}

.exercise-image-gallery {
  margin-top: 1rem;
  display: grid;
  grid-template-columns: 1fr;
  gap: 1.2rem;
}

.exercise-block-title {
  color: var(--green-950);
  font-size: 1.45rem;
  margin-top: 1rem;
  padding-top: 1rem;
  border-top: 1px solid var(--border);
}

.exercise-panel {
  background: var(--white);
  border: 2px solid var(--border);
  border-radius: var(--radius);
  padding: 1.3rem;
  box-shadow: var(--shadow);
  transition: 0.25s ease;
}

.exercise-panel:hover {
  transform: translateY(-4px);
  border-color: var(--green-600, #16a34a);
}

.exercise-panel h3 {
  color: var(--green-900);
  margin-bottom: 0.8rem;
  font-size: 1.1rem;
}

.exercise-panel img {
  width: 100%;
  height: auto;
  border-radius: 12px;
  border: 1px solid var(--border);
  background: #fff;
  margin: 0 auto;
}

.previewable-exercise-image {
  cursor: zoom-in;
  transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.previewable-exercise-image:hover {
  transform: scale(1.01);
  box-shadow: 0 14px 26px rgba(16, 56, 40, 0.12);
}

.exercise-item {
  padding: 1.1rem;
  border-radius: calc(var(--radius) - 4px);
  background: linear-gradient(to bottom, #ffffff, #fbfffc);
}

.exercise-item-header {
  display: flex;
  justify-content: center;
  align-items: flex-start;
  gap: 1rem;
  margin-bottom: 0.75rem;
}

.exercise-item-title-wrap {
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
  gap: 0.4rem;
}

.exercise-nid-badge {
  display: inline-block;
  width: fit-content;
  background: var(--green-100);
  color: var(--green-900);
  border: 1.5px solid var(--green-600, #16a34a);
  border-radius: 999px;
  padding: 0.34rem 0.9rem;
  font-weight: 700;
  letter-spacing: 0.02em;
}

.exercise-description {
  color: var(--muted);
  margin: 0;
}

.exercise-item-actions {
  margin: 0.55rem 0 1rem;
  display: flex;
  justify-content: center;
}

.toggle-correction-btn {
  border: 1.5px solid var(--green-600, #16a34a);
  background: var(--green-100);
  color: var(--green-950);
  font-weight: 600;
  letter-spacing: 0.03em;
  border-radius: 999px;
  padding: 0.5rem 1rem;
  cursor: pointer;
  transition: 0.22s ease;
  white-space: nowrap;
  opacity: 0.92;
  box-shadow: 0 8px 22px rgba(16, 56, 40, 0.08);
}

.toggle-correction-btn:hover {
  background: var(--green-700);
  border-color: var(--green-700);
  color: var(--white);
  opacity: 1;
  transform: translateY(-2px);
}

.toggle-correction-btn[aria-expanded="true"] {
  background: var(--green-700);
  border-color: var(--green-700);
  color: var(--white);
  opacity: 1;
}

.exercise-statement {
  margin-bottom: 0.9rem;
}

.exercise-correction {
  padding-top: 0.9rem;
  border-top: 1px dashed var(--border);
}

.exercise-correction.is-open {
  display: block;
}

/* Evaluation – generate button */
.eval-generate-section {
  display: flex;
  justify-content: center;
  margin: 1.5rem 0 0.5rem;
}

.eval-generate-btn {
  display: flex;
  align-items: center;
  gap: 0.55rem;
  background: var(--green-100);
  color: var(--green-950);
  border: 1.5px solid var(--green-600, #16a34a);
  border-radius: 999px;
  padding: 0.65rem 1.8rem;
  font-size: 1rem;
  font-weight: 600;
  letter-spacing: 0.03em;
  cursor: pointer;
  transition: 0.22s ease;
  box-shadow: 0 8px 22px rgba(16, 56, 40, 0.08);
  opacity: 0.92;
}

.eval-generate-btn::before {
  content: '🎲';
  font-size: 1.1rem;
  line-height: 1;
}

.eval-generate-btn:hover {
  background: var(--green-700);
  border-color: var(--green-700);
  color: var(--white);
  opacity: 1;
  transform: translateY(-2px);
}

.exercise-preview-overlay {
  position: fixed;
  inset: 0;
  z-index: 2000;
  background: rgba(6, 18, 13, 0.72);
  backdrop-filter: blur(2px);
  display: grid;
  place-items: center;
  padding: 2.2rem;
}

.exercise-preview-overlay[hidden] {
  display: none !important;
}

.exercise-preview-dialog {
  width: min(96vw, 1320px);
  max-height: 92vh;
  background: var(--white);
  border-radius: 18px;
  border: 1px solid color-mix(in srgb, var(--green-600, #16a34a) 28%, transparent);
  box-shadow: 0 26px 60px rgba(0, 0, 0, 0.34);
  padding: 1rem;
  overflow: auto;
}

.exercise-preview-dialog img {
  display: block;
  margin: 0 auto;
  max-width: 100%;
  max-height: calc(92vh - 2rem);
  width: auto;
  height: auto;
  border-radius: 12px;
  border: 1px solid var(--border);
}

body.exercise-preview-open {
  overflow: hidden;
}

.level {
  display: inline-block;
  padding: 0.32rem 0.7rem;
  border-radius: 999px;
  font-size: 0.88rem;
  font-weight: 700;
}

.easy {
  background: #e8f6ee;
  color: #256b4d;
}

.medium {
  background: #eef8e6;
  color: #5a7a20;
}

.hard {
  background: #fff3e5;
  color: #9b6117;
}

.expert {
  background: #fceced;
  color: #9a2f3a;
}

/* Footer */
.site-footer {
  border-top: 1px solid var(--border);
  background: var(--white);
}

.footer-content {
  padding: 1.4rem 0;
  text-align: center;
  color: var(--muted);
  font-size: 0.95rem;
}

/* Responsive */
@media (max-width: 1024px) {
  .hero-grid,
  .two-columns {
    grid-template-columns: 1fr;
  }

  .card-grid {
    grid-template-columns: repeat(2, 1fr);
  }

  .exercise-grid {
    grid-template-columns: repeat(2, 1fr);
  }

  .info-grid,
  .stats-grid {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 680px) {
  .nav-container {
    padding: 1rem 0;
    align-items: flex-start;
    flex-direction: column;
  }

  .main-nav {
    width: 100%;
  }

  .main-nav a {
    padding: 0.55rem 0.8rem;
  }

  .main-nav a:last-child {
    display: none;
  }

  .hero {
    padding: 3.5rem 0 3rem;
  }

  .hero-actions {
    flex-direction: column;
    align-items: stretch;
  }

  .card-grid,
  .exercise-grid {
    grid-template-columns: 1fr;
  }

  .exercise-item-header {
    flex-direction: column;
    align-items: stretch;
  }

  .exercise-item-actions {
    justify-content: stretch;
  }

  .toggle-correction-btn {
    width: 100%;
    text-align: center;
  }

  .exercise-preview-overlay {
    padding: 0.8rem;
  }

  .exercise-preview-dialog {
    width: 100%;
    max-height: 94vh;
    padding: 0.65rem;
  }

  .exercise-preview-dialog img {
    max-height: calc(94vh - 1.3rem);
  }

  .section {
    padding: 3rem 0;
  }

  .section-heading h2 {
    font-size: 1.7rem;
  }
}