:root {
  --app-purple: #111111;
  --app-purple-dark: #000000;
  --app-purple-soft: #f3f4f6;
  --app-purple-border: #d1d5db;
  --app-bg: #f8fafc;
  --app-text: #111827;
  --app-muted: #6b7280;
  --app-card: #ffffff;
  --app-radius: 1.1rem;
  --app-shadow: 0 12px 34px rgba(17, 24, 39, 0.08);
}

body {
  min-height: 100vh;
  background:
    radial-gradient(circle at top left, rgba(17, 24, 39, 0.06), transparent 30rem),
    var(--app-bg);
  color: var(--app-text);
}

a { color: var(--app-purple); text-decoration: none; }
a:hover { color: var(--app-purple-dark); }

.app-navbar {
  background: rgba(255, 255, 255, 0.92);
  border-bottom: 1px solid rgba(17, 24, 39, 0.12);
  backdrop-filter: blur(14px);
}

.navbar-brand {
  display: inline-flex;
  align-items: center;
  gap: .55rem;
  font-weight: 800;
  color: var(--app-text);
}

.brand-mark {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 2rem;
  height: 2rem;
  border-radius: .7rem;
  background: var(--app-purple);
  color: #fff;
  font-weight: 800;
}

.navbar .nav-link { color: #374151; font-weight: 500; }
.navbar .nav-link:hover { color: var(--app-purple); }
.navbar-toggler { border-color: var(--app-purple-border); }

.card {
  border: 1px solid rgba(17, 24, 39, 0.12);
  border-radius: var(--app-radius);
  background: var(--app-card);
  box-shadow: var(--app-shadow);
}

.card-header:first-child { border-radius: var(--app-radius) var(--app-radius) 0 0; }
.card-footer:last-child { border-radius: 0 0 var(--app-radius) var(--app-radius); }

.btn { border-radius: .8rem; font-weight: 600; }
.btn-primary,
.btn-success {
  background: var(--app-purple);
  border-color: var(--app-purple);
}
.btn-primary:hover,
.btn-success:hover {
  background: var(--app-purple-dark);
  border-color: var(--app-purple-dark);
}
.btn-outline-primary {
  border-color: var(--app-purple);
  color: var(--app-purple);
}
.btn-outline-primary:hover {
  background: var(--app-purple);
  border-color: var(--app-purple);
  color: #fff;
}

.form-control,
.form-select {
  border-radius: .85rem;
  border-color: #d1d5db;
}
.form-control:focus,
.form-select:focus {
  border-color: var(--app-purple);
  box-shadow: 0 0 0 .22rem rgba(109, 40, 217, .14);
}

.page-hero {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 1rem;
  padding: 1.4rem;
  border: 1px solid rgba(17, 24, 39, 0.12);
  border-radius: 1.35rem;
  background: linear-gradient(135deg, #fff 0%, #f9fafb 100%);
  box-shadow: var(--app-shadow);
}

.hero-actions,
.teacher-toolbar {
  display: flex;
  gap: .6rem;
  flex-wrap: wrap;
  justify-content: flex-end;
}

.eyebrow {
  display: inline-block;
  margin-bottom: .35rem;
  color: var(--app-purple);
  font-size: .75rem;
  font-weight: 800;
  letter-spacing: .08em;
  text-transform: uppercase;
}

.metric-card .card-body { min-height: 8rem; }
.metric-label { color: var(--app-muted); font-size: .9rem; }
.metric-value { font-size: 2.35rem; font-weight: 800; line-height: 1.05; color: var(--app-purple-dark); }

.action-card,
.topic-card {
  color: inherit;
  transition: transform .15s ease, border-color .15s ease, box-shadow .15s ease;
}
.action-card:hover,
.topic-card:hover {
  transform: translateY(-2px);
  border-color: var(--app-purple-border);
  box-shadow: 0 16px 38px rgba(17, 24, 39, 0.13);
}
.action-card p { color: var(--app-muted); margin-bottom: 0; }

.badge-soft {
  color: var(--app-purple-dark);
  background: var(--app-purple-soft);
  border: 1px solid var(--app-purple-border);
}

.task-type-pill {
  display: inline-flex;
  align-items: center;
  width: fit-content;
  padding: .25rem .55rem;
  border-radius: 999px;
  color: var(--app-purple-dark);
  background: var(--app-purple-soft);
  border: 1px solid var(--app-purple-border);
  font-size: .78rem;
  font-weight: 700;
}

.task-context {
  border-left: 4px solid var(--app-purple);
  background: #f9fafb;
  border-radius: .85rem;
  padding: .95rem 1rem;
  white-space: pre-wrap;
  font-size: 1.02rem;
}

.answer-option {
  display: flex;
  gap: .65rem;
  align-items: flex-start;
  width: 100%;
  padding: .85rem 1rem;
  border: 1px solid #e5e7eb;
  border-radius: .9rem;
  cursor: pointer;
  transition: border-color .15s ease, background .15s ease;
}
.answer-option:hover {
  background: #f9fafb;
  border-color: var(--app-purple-border);
}

.checkbox-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: .45rem 1rem;
  background: #fff;
}

.code-textarea {
  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, "Liberation Mono", monospace;
  font-size: .9rem;
  min-height: 32rem;
}

.sticky-help,
.sticky-preview { position: sticky; top: 5.25rem; }
.preview-scroll { max-height: calc(100vh - 8rem); overflow: auto; }
.preview-box { padding: .8rem; background: #ffffff; border: 1px solid #e5e7eb; border-radius: .9rem; }

.markdown-body { line-height: 1.7; }
.markdown-body h1,
.markdown-body h2,
.markdown-body h3,
.markdown-body h4 {
  margin-top: 1rem;
  margin-bottom: .65rem;
  font-weight: 800;
  color: #111827;
}
.markdown-body h1 { font-size: 1.55rem; }
.markdown-body h2 { font-size: 1.35rem; }
.markdown-body h3 { font-size: 1.15rem; }
.markdown-body p:last-child,
.markdown-body ul:last-child,
.markdown-body ol:last-child { margin-bottom: 0; }
.markdown-body blockquote {
  margin: 1rem 0;
  padding: .85rem 1rem;
  border-left: 4px solid var(--app-purple);
  border-radius: .8rem;
  background: #f9fafb;
  color: #374151;
}
.markdown-body code {
  color: var(--app-purple-dark);
  background: var(--app-purple-soft);
  border: 1px solid var(--app-purple-border);
  border-radius: .35rem;
  padding: .08rem .3rem;
}
.markdown-body pre {
  background: #111827;
  color: #f9fafb;
  border-radius: .9rem;
  padding: 1rem;
  overflow: auto;
}
.markdown-body pre code { color: inherit; background: transparent; border: 0; padding: 0; }

.matching-row {
  padding: .65rem;
  border: 1px solid #e5e7eb;
  border-radius: .9rem;
  background: #fff;
}

.result-hero { background: linear-gradient(135deg, #fff, #f9fafb); }

.progress { height: .8rem; border-radius: 999px; background: #e5e7eb; }
.progress-bar { background: var(--app-purple); border-radius: 999px; }

.sticky-submit {
  position: sticky;
  bottom: 0;
  z-index: 10;
  margin: 1.5rem -0.25rem 0;
  padding: 1rem .25rem;
  background: linear-gradient(180deg, rgba(248, 250, 252, 0), rgba(248, 250, 252, .95) 30%, rgba(248, 250, 252, 1));
}

.app-footer {
  padding: 1.2rem 0 2rem;
  border-top: 1px solid rgba(17, 24, 39, 0.12);
}

@media (max-width: 991.98px) {
  .page-hero { flex-direction: column; padding: 1rem; }
  .hero-actions,
  .teacher-toolbar { width: 100%; justify-content: stretch; }
  .hero-actions .btn,
  .teacher-toolbar .btn { flex: 1 1 auto; }
  .sticky-help,
  .sticky-preview { position: static; }
  .preview-scroll { max-height: none; }
}

@media (max-width: 575.98px) {
  main.container { padding-left: .9rem; padding-right: .9rem; }
  .metric-value { font-size: 1.8rem; }
  .checkbox-grid { grid-template-columns: 1fr; }
  .code-textarea { min-height: 24rem; font-size: .82rem; }
  .table { font-size: .88rem; }
  .btn-lg { width: 100%; }
  .answer-option { padding: .75rem .85rem; }
}