/* Spreadsheet grid */
.ws {
  display: flex; flex-direction: column;
  border: 1px solid var(--border);
  border-radius: var(--r-md);
  background: var(--surface);
  overflow: hidden;
  font-family: var(--font-sans);
  font-size: 14px;
  user-select: none;
}
.ws-toolbar {
  display: flex; align-items: center; gap: 8px;
  padding: 8px 10px; border-bottom: 1px solid var(--border);
  background: var(--surface-2); flex-wrap: wrap;
}
.ws-fx {
  display: flex; align-items: center; gap: 8px;
  padding: 8px 10px; border-bottom: 1px solid var(--border);
  background: var(--surface);
}
.ws-fx .addr {
  min-width: 70px; padding: 6px 8px; border: 1px solid var(--border);
  border-radius: 8px; font-family: var(--font-mono); font-size: 13px;
  background: var(--surface-2);
}
.ws-fx .fx-label { font-family: var(--font-mono); font-weight: 700; color: var(--brand); padding: 0 4px; }
.ws-fx input.fx-input {
  flex: 1; padding: 8px 12px; border: 1px solid var(--border);
  border-radius: 8px; font: inherit; font-family: var(--font-mono);
}
.ws-grid-wrap { overflow: auto; max-height: 460px; }
.ws-grid { border-collapse: collapse; width: max-content; }
.ws-grid th, .ws-grid td { border: 1px solid var(--border); height: 30px; min-width: 96px; padding: 4px 8px; vertical-align: middle; }
.ws-grid th {
  background: var(--surface-2); color: var(--text-muted);
  font-weight: 600; text-align: center; font-size: 12px;
  position: sticky; top: 0; z-index: 2;
}
.ws-grid th.row-h { left: 0; z-index: 3; min-width: 40px; }
.ws-grid td { background: #fff; cursor: cell; position: relative; }
.ws-grid td.num { text-align: right; font-variant-numeric: tabular-nums; }
.ws-grid td.bold { font-weight: 700; }
.ws-grid td.italic { font-style: italic; }
.ws-grid td.center { text-align: center; }
.ws-grid td.right { text-align: right; }
.ws-grid td.fill-yellow { background: #FFF7C2; }
.ws-grid td.fill-green  { background: #DEFBEC; }
.ws-grid td.fill-blue   { background: #E0F0FF; }
.ws-grid td.fill-pink   { background: #FFE0EC; }
.ws-grid td.error  { color: var(--danger); font-weight: 600; }
.ws-grid td.selected {
  outline: 2px solid var(--brand); outline-offset: -2px;
  background: var(--brand-soft);
}
.ws-grid td.editing { padding: 0; }
.ws-grid td input.cell-input {
  width: 100%; height: 100%; border: none; outline: none;
  padding: 4px 8px; font: inherit; font-family: var(--font-mono);
  background: #FFFEEB;
}
.ws-status {
  padding: 6px 12px; font-size: 12px;
  border-top: 1px solid var(--border); color: var(--text-muted);
  background: var(--surface-2);
  display: flex; justify-content: space-between;
}
.ws-btn {
  padding: 4px 10px; border-radius: 6px; border: 1px solid var(--border);
  background: #fff; cursor: pointer; font: inherit; font-size: 12px; font-weight: 600;
}
.ws-btn:hover { background: var(--surface-2); }
.ws-btn.active { background: var(--brand); color: #fff; border-color: var(--brand); }

/* Lesson layout */
.lesson-layout {
  display: grid; grid-template-columns: 280px 1fr;
  min-height: calc(100vh - 60px);
  background: var(--bg);
}
.lesson-sidebar {
  background: var(--surface); border-right: 1px solid var(--border);
  padding: 18px 0; overflow-y: auto;
}
.lesson-sidebar .mod-title {
  padding: 10px 20px 6px; font-size: 12px; font-weight: 700;
  color: var(--text-dim); text-transform: uppercase; letter-spacing: .05em;
}
.lesson-sidebar button.mod-toggle {
  display: flex; align-items: center; gap: 8px; width: 100%;
  background: transparent; border: 0; cursor: pointer; text-align: left;
  margin-top: 6px;
}
.lesson-sidebar button.mod-toggle:hover { color: var(--text); }
.lesson-sidebar .mod-toggle .mod-caret {
  display: inline-block; transition: transform .15s ease; font-size: 10px; opacity: .7;
}
.lesson-sidebar .mod-toggle.collapsed .mod-caret { transform: rotate(-90deg); }
.lesson-sidebar .mod-toggle .mod-name { flex: 1; }
.lesson-sidebar .mod-toggle .mod-count {
  font-size: 11px; color: var(--text-dim); font-weight: 600; letter-spacing: 0;
  text-transform: none; background: var(--surface-2); padding: 2px 8px; border-radius: 999px;
}
.lesson-sidebar .mod-lessons.hidden { display: none; }
.lesson-sidebar .mod-bulk {
  display: flex; align-items: center; gap: 6px;
  padding: 4px 20px 10px; border-bottom: 1px solid var(--border); margin-bottom: 6px;
}
.lesson-sidebar .mod-bulk-btn {
  background: transparent; border: 0; cursor: pointer; padding: 2px 4px;
  font-size: 11px; font-weight: 600; color: var(--text-dim);
  text-transform: uppercase; letter-spacing: .04em;
}
.lesson-sidebar .mod-bulk-btn:hover { color: var(--brand); }
.lesson-sidebar .mod-bulk-sep { color: var(--text-dim); font-size: 11px; }
.lesson-sidebar a.lesson-link {
  display: flex; align-items: center; gap: 10px;
  padding: 8px 20px; color: var(--text); text-decoration: none; font-size: .9rem;
  border-left: 3px solid transparent;
}
.lesson-sidebar a.lesson-link:hover { background: var(--surface-2); }
.lesson-sidebar a.lesson-link.active { background: var(--brand-soft); color: var(--brand); border-left-color: var(--brand); font-weight: 600; }
.lesson-sidebar a.lesson-link .ic { font-size: 1rem; opacity: .7; width: 18px; }
.lesson-sidebar a.lesson-link.done .ic { color: var(--success); opacity: 1; }

.lesson-main { padding: 32px clamp(20px, 4vw, 56px) 80px; max-width: 1100px; }
.lesson-main h1 { margin: 0 0 4px; }
.lesson-main .crumb { color: var(--text-muted); font-size: .9rem; margin-bottom: 12px; }
.lesson-content { font-size: 1.04rem; line-height: 1.7; }
.lesson-content h2 { margin-top: 2rem; }
.lesson-content code { background: var(--surface-2); color: var(--text); padding: 2px 6px; border-radius: 6px; font-family: var(--font-mono); font-size: .92em; }
.lesson-content pre { background: var(--text); color: #fff; padding: 14px 16px; border-radius: var(--r-md); overflow-x: auto; }
.lesson-content pre code { background: transparent; color: inherit; padding: 0; border-radius: 0; font-size: .95em; }
.lesson-content blockquote { border-left: 4px solid var(--brand); margin: 1rem 0; padding: .4rem 1rem; background: var(--brand-soft); border-radius: 0 var(--r-md) var(--r-md) 0; }

.exercise-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--r-lg);
  padding: 22px;
  margin-top: 24px;
}
.exercise-card h3 { margin-top: 0; }
.exercise-instructions ol { padding-left: 20px; }
.exercise-instructions li { margin: .35rem 0; }

.feedback {
  margin-top: 14px; padding: 12px 16px; border-radius: var(--r-md);
  display: none;
}
.feedback.ok   { display: block; background: #DEFBEC; color: #0A7C44; border: 1px solid #6FE0A7; }
.feedback.bad  { display: block; background: #FFE0E8; color: #A4253F; border: 1px solid #FFA8BB; }
.feedback ul { margin: 6px 0 0; padding-left: 18px; }

.lesson-footer-nav {
  display: flex; justify-content: space-between; gap: 12px;
  margin-top: 32px;
}

@media (max-width: 880px) {
  .lesson-layout { grid-template-columns: 1fr; }
  .lesson-sidebar { border-right: none; border-bottom: 1px solid var(--border); max-height: 240px; }
}