/* ============================================================
   NEXORA · Screen / Lesson
   ============================================================ */

.lesson-screen { display: block; }

.lsn-layout {
  display: grid;
  grid-template-columns: 264px minmax(0, 1fr);
  gap: var(--content-gutter);
  align-items: start;
}

/* ---------- sidebar ------------------------------------------ */

.lsn-side {
  position: sticky;
  top: calc(var(--tb-top) + var(--tb-h) + 1.4rem);
  max-height: calc(100vh - var(--tb-top) - var(--tb-h) - 3rem);
  display: flex;
  flex-direction: column;
  border-radius: var(--radius-lg);
  background: var(--glass-bg);
  box-shadow: var(--depth), var(--glass-edge);
  overflow: hidden;
}

.lsn-side-head {
  padding: 1rem 1.1rem;
  border-bottom: 1px solid var(--border);
  flex: none;
}

.lsn-back {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  font-family: var(--font-mono);
  font-size: 0.68rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--text-3);
  margin-bottom: 0.6rem;
  transition: color var(--dur-fast);
}

.lsn-back:hover { color: var(--accent-2); }
.lsn-back .icon { transform: rotate(180deg); }

.lsn-side-head h3 { font-size: 1.05rem; margin-bottom: 0.7rem; }

.lsn-side-progress {
  display: flex;
  align-items: center;
  gap: 0.6rem;
}

.lsn-side-progress .bar { flex: 1; }
.lsn-side-progress .mono { font-size: 0.7rem; color: var(--accent-2); }

.lsn-toc {
  flex: 1;
  min-height: 0;
  overflow-y: auto;
  padding: 0.6rem;
}

.lsn-mod {
  font-family: var(--font-mono);
  font-size: 0.6rem;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--text-3);
  padding: 0.7rem 0.6rem 0.35rem;
}

.lsn-item {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  padding: 0.5rem 0.6rem;
  border-radius: var(--radius-sm);
  font-size: 0.86rem;
  color: var(--text-2);
  transition: color var(--dur-fast), background var(--dur-fast);
}

.lsn-item:hover { color: var(--text-1); background: rgba(255, 255, 255, 0.06); }

.lsn-item.is-current {
  color: var(--text-1);
  background: linear-gradient(90deg, color-mix(in srgb, var(--accent) 20%, transparent), color-mix(in srgb, var(--accent) 8%, transparent));
  box-shadow: inset 0 0 0 1px var(--border-accent);
}

.lsn-dot {
  display: grid;
  place-items: center;
  width: 18px;
  height: 18px;
  flex: none;
  border-radius: 50%;
  font-size: 0.55rem;
  color: var(--text-3);
  box-shadow: inset 0 0 0 1px var(--border-strong);
}

.lsn-dot .icon { width: 0.7em; height: 0.7em; }
.lsn-dot.done { color: var(--success-text); background: var(--success-soft); box-shadow: inset 0 0 0 1px color-mix(in srgb, var(--success) 45%, transparent); }
.lsn-dot.current { color: var(--accent-text); background: var(--accent-soft); box-shadow: inset 0 0 0 1px color-mix(in srgb, var(--accent) 55%, transparent); }

.lsn-item span { flex: 1; min-width: 0; }

/* ---------- main --------------------------------------------- */

.lsn-main { min-width: 0; }

.lsn-crumbs {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  flex-wrap: wrap;
  font-family: var(--font-mono);
  font-size: 0.68rem;
  color: var(--text-3);
  margin-bottom: 0.9rem;
}

.lsn-crumbs a { color: var(--text-3); transition: color var(--dur-fast); }
.lsn-crumbs a:hover { color: var(--accent-2); }
.lsn-crumbs b { color: var(--text-2); font-weight: 500; }

.lsn-head {
  padding-bottom: 1.3rem;
  border-bottom: 1px solid var(--border);
  margin-bottom: 1.6rem;
}

.lsn-head h1 {
  font-size: clamp(1.6rem, 1.3rem + 1.6vw, 2.2rem);
  letter-spacing: -0.03em;
  margin-bottom: 0.6rem;
}

.lsn-summary {
  font-size: 1.02rem;
  line-height: 1.65;
  color: var(--text-2);
  max-width: 68ch;
  margin-bottom: 0.9rem;
}

.lsn-meta {
  display: flex;
  gap: 0.5rem;
  flex-wrap: wrap;
  align-items: center;
  margin-bottom: 0.9rem;
}

.lsn-meta .badge { font-size: 0.64rem; }

.lsn-prereq {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  font-family: var(--font-mono);
  font-size: 0.66rem;
  color: var(--text-3);
}

.lsn-prereq a { color: var(--accent-2); }
.lsn-prereq a:hover { text-decoration: underline; }

.lsn-actions { display: flex; gap: 0.5rem; flex-wrap: wrap; }
.le-btn.is-on { color: var(--gold); background: var(--achievement-soft); }

.lsn-note {
  margin-top: 0.9rem;
  padding: 0.9rem 1rem;
  border-radius: var(--radius-md);
  background: var(--glass-bg);
  box-shadow: var(--depth), var(--glass-edge);
}

.lsn-note textarea {
  width: 100%;
  margin-top: 0.4rem;
  padding: 0.6rem 0.75rem;
  border: 0;
  border-radius: var(--radius-sm);
  background: rgba(255, 255, 255, 0.06);
  color: var(--text-1);
  font-family: var(--font-body);
  font-size: 0.9rem;
  line-height: 1.6;
  resize: vertical;
  outline: none;
}

.lsn-note textarea:focus { box-shadow: 0 0 0 2px var(--accent); }

.lsn-note-status {
  display: block;
  margin-top: 0.4rem;
  font-family: var(--font-mono);
  font-size: 0.66rem;
  color: var(--success);
  min-height: 1em;
}

/* ---------- footer ------------------------------------------- */

.lsn-foot {
  margin-top: 2rem;
  padding-top: 1.4rem;
  border-top: 1px solid var(--border);
  display: grid;
  gap: 1.2rem;
}

.lsn-check {
  display: inline-flex;
  align-items: center;
  gap: 0.7rem;
  cursor: pointer;
  padding: 0.9rem 1.1rem;
  border-radius: var(--radius-md);
  background: var(--glass-bg);
  box-shadow: var(--depth), var(--glass-edge);
  width: 100%;
}

.lsn-check input { position: absolute; opacity: 0; width: 0; height: 0; }

.lsn-check-box {
  display: grid;
  place-items: center;
  width: 24px;
  height: 24px;
  flex: none;
  border-radius: 7px;
  color: transparent;
  background: rgba(255, 255, 255, 0.07);
  box-shadow: inset 0 0 0 1px var(--border-strong);
  transition: all var(--dur) var(--ease-spring);
}

.lsn-check input:checked + .lsn-check-box {
  color: var(--accent-on);
  background: var(--gradient-brand);
  box-shadow: 0 6px 16px -6px var(--glow-accent);
}

.lsn-check input:focus-visible + .lsn-check-box { outline: 2px solid var(--accent); outline-offset: 2px; }
.lsn-check-label { font-size: 0.95rem; color: var(--text-2); }
.lsn-check input:checked ~ .lsn-check-label { color: var(--success); }

.lsn-nav {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.8rem;
}

.lsn-nav-btn {
  display: flex;
  align-items: center;
  gap: 0.8rem;
  padding: 1rem 1.1rem;
  border-radius: var(--radius-md);
  background: var(--glass-bg);
  box-shadow: var(--depth), var(--glass-edge);
  transition: transform var(--dur), box-shadow var(--dur);
}

.lsn-nav-btn:hover {
  transform: translateY(-2px);
  box-shadow: var(--depth), var(--glass-edge), 0 0 22px -8px var(--glow-accent);
}

.lsn-nav-btn.next { text-align: right; flex-direction: row-reverse; }
.lsn-nav-btn .icon { flex: none; color: var(--accent-2); }
.lsn-nav-btn.prev .icon { transform: rotate(180deg); }
.lsn-nav-btn div { flex: 1; min-width: 0; }

.lsn-nav-btn small {
  display: block;
  font-family: var(--font-mono);
  font-size: 0.62rem;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--text-3);
}

.lsn-nav-btn b {
  display: block;
  font-family: var(--font-display);
  font-size: 0.94rem;
  color: var(--text-1);
  margin-top: 0.15rem;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.lsn-nav-empty { opacity: 0.35; pointer-events: none; }

/* ---------- mobile drawer ------------------------------------ */

.lsn-drawer-btn {
  display: none;
  align-items: center;
  gap: 0.5rem;
  padding: 0.6rem 1rem;
  margin-bottom: 0.9rem;
  border-radius: var(--radius-md);
  font-family: var(--font-display);
  font-size: 0.86rem;
  color: var(--text-1);
  background: var(--glass-bg);
  box-shadow: var(--depth), var(--glass-edge);
}

@media (max-width: 1000px) {
  .lsn-layout { grid-template-columns: 1fr; }
  .lsn-drawer-btn { display: inline-flex; }

  .lsn-side {
    position: fixed;
    inset: 0 auto 0 0;
    z-index: 150;
    width: min(84vw, 320px);
    max-height: none;
    border-radius: 0 var(--radius-lg) var(--radius-lg) 0;
    transform: translateX(-102%);
    transition: transform var(--dur) var(--ease-out);
  }

  .lsn-side.is-open { transform: none; }
}

@media (max-width: 640px) {
  .lsn-nav { grid-template-columns: 1fr; }
}

/* ---------- revision check-in (spaced repetition, student wording) ---- */
.lsn-review-check { display: grid; gap: .6rem; padding: 1.1rem 1.2rem; margin-top: 1.2rem; }
.lsn-review-check h3 { font-size: 1rem; color: var(--text-1); }
.lsn-review-check p { font-size: .85rem; color: var(--text-2); line-height: 1.5; }
.lsn-review-actions { display: flex; gap: .5rem; flex-wrap: wrap; margin-top: .2rem; }
.lsn-review-actions .btn { flex: 1 1 auto; min-height: 40px; justify-content: center; }