/* === VARIABLES === */
:root {
  --bg: #1a1b26;
  --bg2: #24283b;
  --bg3: #2f3349;
  --fg: #c0caf5;
  --fg-dim: #565f89;
  --accent: #7aa2f7;
  --accent2: #bb9af7;
  --green: #9ece6a;
  --red: #f7768e;
  --yellow: #e0af68;
  --orange: #ff9e64;
  --cyan: #7dcfff;
  --border: #3b4261;
  --font-mono: 'JetBrains Mono', 'Fira Code', 'Cascadia Code', 'Consolas', monospace;
  --font-sans: -apple-system, BlinkMacSystemFont, 'Segoe UI', system-ui, sans-serif;
  --radius: 8px;
  --shadow: 0 2px 8px rgba(0,0,0,0.3);
}

[data-theme="light"] {
  --bg: #f0f0f5;
  --bg2: #ffffff;
  --bg3: #e8e8ef;
  --fg: #1a1b26;
  --fg-dim: #9099b0;
  --border: #d0d0dd;
  --shadow: 0 2px 8px rgba(0,0,0,0.1);
}

/* === RESET === */
* { margin: 0; padding: 0; box-sizing: border-box; }
body {
  font-family: var(--font-sans);
  background: var(--bg);
  color: var(--fg);
  min-height: 100vh;
  overflow: hidden;
  -webkit-text-size-adjust: 100%;
  -webkit-tap-highlight-color: transparent;
}

/* === NAV === */
#topnav {
  display: flex;
  align-items: center;
  padding: 0 20px;
  height: 50px;
  background: var(--bg2);
  border-bottom: 1px solid var(--border);
  gap: 20px;
}
.nav-brand {
  cursor: pointer;
  display: flex;
  align-items: baseline;
  gap: 2px;
}
.logo-mark {
  font-family: var(--font-mono);
  font-size: 20px;
  font-weight: 400;
  color: var(--fg-dim);
  letter-spacing: -0.5px;
}
.logo-mark strong {
  font-weight: 800;
  color: var(--accent);
}
.nav-version {
  font-family: var(--font-mono);
  font-size: 11px;
  color: var(--fg-dim);
  background: var(--bg3);
  padding: 2px 8px;
  border-radius: 10px;
}
.nav-tabs {
  display: flex;
  gap: 4px;
}
.nav-tab {
  background: none;
  border: none;
  color: var(--fg-dim);
  padding: 8px 16px;
  border-radius: var(--radius);
  cursor: pointer;
  font-size: 14px;
  transition: all 0.2s;
}
.nav-tab:hover { background: var(--bg3); color: var(--fg); }
.nav-tab.active { background: var(--accent); color: #fff; }
.nav-right {
  margin-left: auto;
  display: flex;
  align-items: center;
  gap: 12px;
}
#progress-badge {
  font-family: var(--font-mono);
  font-size: 13px;
  color: var(--green);
  background: var(--bg3);
  padding: 4px 10px;
  border-radius: 12px;
}
.theme-toggle {
  background: none;
  border: none;
  font-size: 18px;
  cursor: pointer;
  padding: 4px;
}

/* === MODE PANELS === */
.mode-panel { display: none; height: calc(100vh - 50px); }
.mode-panel.active { display: flex; }

/* === LEARN MODE === */
#mode-learn { display: none; }
#mode-learn.active { display: flex; }

#lesson-sidebar {
  width: 280px;
  min-width: 280px;
  background: var(--bg2);
  border-right: 1px solid var(--border);
  overflow-y: auto;
  padding: 12px;
}
.sidebar-header { margin-bottom: 12px; }
#lesson-search {
  width: 100%;
  padding: 8px 12px;
  background: var(--bg3);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  color: var(--fg);
  font-size: 13px;
  outline: none;
}
#lesson-search:focus { border-color: var(--accent); }

.lesson-category {
  margin-bottom: 8px;
}
.lesson-category-title {
  font-size: 11px;
  text-transform: uppercase;
  letter-spacing: 1px;
  color: var(--fg-dim);
  padding: 8px 8px 4px;
  font-weight: 600;
}
.lesson-item {
  padding: 8px 12px;
  border-radius: 6px;
  cursor: pointer;
  font-size: 13px;
  display: flex;
  align-items: center;
  gap: 8px;
  transition: background 0.15s;
}
.lesson-item:hover { background: var(--bg3); }
.lesson-item.active { background: var(--accent); color: #fff; }
.lesson-item .check { color: var(--green); font-size: 14px; }
.lesson-item .check.pending { color: var(--fg-dim); }

#lesson-content {
  flex: 1;
  overflow-y: auto;
  padding: 24px 48px;
}
#lesson-content > #lesson-header,
#lesson-content > #lesson-explanation {
  max-width: 900px;
}
#lesson-header { margin-bottom: 20px; }
#lesson-title { font-size: 28px; font-weight: 700; color: var(--accent); }
#lesson-desc { color: var(--fg-dim); margin-top: 4px; font-size: 15px; }
#lesson-explanation {
  margin-bottom: 20px;
  line-height: 1.7;
  font-size: 15px;
}
#lesson-explanation code {
  background: var(--bg3);
  padding: 2px 6px;
  border-radius: 4px;
  font-family: var(--font-mono);
  font-size: 13px;
  color: var(--cyan);
}
#lesson-explanation pre {
  background: var(--bg3);
  padding: 12px 16px;
  border-radius: var(--radius);
  overflow-x: auto;
  font-family: var(--font-mono);
  font-size: 13px;
  margin: 12px 0;
  border: 1px solid var(--border);
}
#lesson-explanation h3 {
  color: var(--accent2);
  margin: 16px 0 8px;
  font-size: 16px;
}
#lesson-explanation p { margin: 8px 0; }
#lesson-explanation ul, #lesson-explanation ol {
  margin: 8px 0 8px 24px;
}
#lesson-explanation li { margin: 4px 0; }

/* === EXERCISE PANELS === */
.exercise-area { margin-top: 20px; }
.exercise-panels {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
}
.panel {
  background: var(--bg2);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
}
.panel-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 8px 12px;
  background: var(--bg3);
  font-size: 12px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  color: var(--fg-dim);
}
.panel textarea, .panel input[type="text"] {
  width: 100%;
  padding: 12px;
  background: var(--bg2);
  border: none;
  color: var(--fg);
  font-family: var(--font-mono);
  font-size: 14px;
  resize: none;
  outline: none;
}
.panel textarea { height: 150px; }
.panel input[type="text"] {
  border-top: 1px solid var(--border);
  padding: 10px 12px;
}
.panel input[type="text"]:focus { background: var(--bg3); }
.output-area {
  padding: 12px;
  font-family: var(--font-mono);
  font-size: 14px;
  min-height: 100px;
  max-height: 200px;
  overflow: auto;
  white-space: pre-wrap;
  word-break: break-word;
}
.output-area.expected { color: var(--green); background: rgba(158, 206, 106, 0.05); }
.output-area.placeholder { color: var(--fg-dim); font-style: italic; }
.output-area.error { color: var(--red); }
.output-area.success { border: 2px solid var(--green); }

/* === BUTTONS === */
.btn {
  padding: 8px 20px;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--bg2);
  color: var(--fg);
  cursor: pointer;
  font-size: 14px;
  transition: all 0.15s;
}
.btn:hover { background: var(--bg3); }
.btn-primary { background: var(--accent); color: #fff; border-color: var(--accent); }
.btn-primary:hover { opacity: 0.9; }
.btn-sm {
  padding: 4px 10px;
  border: 1px solid var(--border);
  border-radius: 4px;
  background: transparent;
  color: var(--fg-dim);
  cursor: pointer;
  font-size: 11px;
}
.btn-sm:hover { background: var(--bg3); color: var(--fg); }
.btn-sm.btn-primary { background: var(--accent); color: #fff; border-color: var(--accent); }
.lesson-nav {
  display: flex;
  justify-content: space-between;
  margin-top: 16px;
  padding-top: 16px;
  border-top: 1px solid var(--border);
}

/* === HINT === */
.hint-btn {
  cursor: pointer;
  font-size: 12px;
  color: var(--yellow);
  user-select: none;
}
.hint-btn:hover { opacity: 0.8; }
.hint-box {
  padding: 8px 12px;
  background: rgba(224, 175, 104, 0.1);
  border-left: 3px solid var(--yellow);
  font-size: 13px;
  font-family: var(--font-mono);
  color: var(--yellow);
}
.hidden { display: none; }

/* === PLAYGROUND === */
.playground-layout {
  display: grid;
  grid-template-columns: 1fr 1fr;
  grid-template-rows: auto 1fr;
  gap: 0;
  height: 100%;
  width: 100%;
}
.pg-left, .pg-right {
  border: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  min-height: 0;
}
.pg-left textarea, .pg-right pre {
  flex: 1;
  padding: 16px;
  background: var(--bg2);
  border: none;
  color: var(--fg);
  font-family: var(--font-mono);
  font-size: 14px;
  resize: none;
  outline: none;
  overflow: auto;
  min-height: 0;
}
.pg-middle {
  grid-column: 1 / -1;
  border: 1px solid var(--border);
  background: var(--bg2);
  order: -1;
}
.pg-middle input {
  width: 100%;
  padding: 14px 20px;
  background: var(--bg);
  border: none;
  border-bottom: 2px solid var(--accent);
  color: var(--accent);
  font-family: var(--font-mono);
  font-size: 18px;
  font-weight: 600;
  outline: none;
}
.pg-middle input:focus { background: var(--bg3); }
.pg-options {
  display: flex;
  gap: 12px;
  font-size: 12px;
  font-family: var(--font-mono);
}
.pg-options label { display: flex; align-items: center; gap: 4px; cursor: pointer; color: var(--fg-dim); }
.pg-options input[type="checkbox"] { accent-color: var(--accent); }
#pg-time { font-family: var(--font-mono); font-size: 11px; color: var(--fg-dim); }
.history-list {
  display: flex;
  gap: 6px;
  padding: 6px 12px;
  overflow-x: auto;
  font-size: 12px;
}
.history-item {
  background: var(--bg3);
  padding: 3px 8px;
  border-radius: 4px;
  cursor: pointer;
  font-family: var(--font-mono);
  white-space: nowrap;
  color: var(--fg-dim);
  border: none;
}
.history-item:hover { color: var(--fg); }

/* === CHALLENGES === */
.challenges-layout {
  display: flex;
  height: 100%;
  width: 100%;
}
#challenge-sidebar {
  width: 280px;
  min-width: 280px;
  background: var(--bg2);
  border-right: 1px solid var(--border);
  overflow-y: auto;
  padding: 16px;
}
#challenge-sidebar h3 { margin-bottom: 12px; }
#challenge-content {
  flex: 1;
  overflow-y: auto;
  padding: 24px 48px;
}
#ch-difficulty {
  display: inline-block;
  padding: 2px 10px;
  border-radius: 12px;
  font-size: 12px;
  font-weight: 600;
}
.diff-easy { background: rgba(158,206,106,0.2); color: var(--green); }
.diff-medium { background: rgba(224,175,104,0.2); color: var(--yellow); }
.diff-hard { background: rgba(247,118,142,0.2); color: var(--red); }
.diff-expert { background: rgba(187,154,247,0.2); color: var(--accent2); }
.challenge-item {
  padding: 8px 12px;
  border-radius: 6px;
  cursor: pointer;
  font-size: 13px;
  display: flex;
  align-items: center;
  gap: 8px;
  margin-bottom: 4px;
}
.challenge-item:hover { background: var(--bg3); }
.challenge-item.active { background: var(--accent); color: #fff; }
.challenge-item .ch-diff {
  font-size: 10px;
  padding: 1px 6px;
  border-radius: 8px;
  margin-left: auto;
}
#ch-result {
  margin-top: 16px;
  padding: 16px;
  border-radius: var(--radius);
  font-size: 15px;
  font-weight: 600;
  text-align: center;
}
#ch-result.correct {
  background: rgba(158,206,106,0.15);
  color: var(--green);
  border: 2px solid var(--green);
}
#ch-result.incorrect {
  background: rgba(247,118,142,0.1);
  color: var(--red);
  border: 2px solid var(--red);
}

/* === VISUALIZER === */
.viz-layout {
  display: grid;
  grid-template-columns: 240px 1fr;
  grid-template-rows: auto 1fr;
  height: 100%;
  width: 100%;
  overflow: hidden;
}
.viz-input-section {
  grid-row: 1 / -1;
  display: flex;
  flex-direction: column;
  border-right: 1px solid var(--border);
  background: var(--bg2);
  overflow: hidden;
}
.viz-input-section textarea {
  flex: 1;
  padding: 12px;
  background: var(--bg2);
  border: none;
  color: var(--fg);
  font-family: var(--font-mono);
  font-size: 13px;
  resize: none;
  outline: none;
  min-height: 0;
}
.viz-filter-section {
  display: flex;
  align-items: stretch;
  border-bottom: 2px solid var(--accent);
  background: var(--bg2);
}
.viz-filter-section input {
  flex: 1;
  padding: 14px 20px;
  background: var(--bg);
  border: none;
  color: var(--accent);
  font-family: var(--font-mono);
  font-size: 18px;
  font-weight: 600;
  outline: none;
}
.viz-filter-section input:focus { background: var(--bg3); }
.viz-run-btn {
  padding: 0 24px;
  border: none;
  border-left: 1px solid var(--border);
  border-radius: 0;
  font-size: 14px;
  font-weight: 600;
  cursor: pointer;
  white-space: nowrap;
}
.viz-run-btn:hover { opacity: 0.9; }

.viz-pipeline {
  overflow-y: auto;
  overflow-x: hidden;
  padding: 16px 24px;
  background: var(--bg);
  min-height: 0;
  min-width: 0;
}
.viz-empty {
  text-align: center;
  padding: 48px 24px;
  color: var(--fg-dim);
}
.viz-empty p { margin: 8px 0; }
.viz-empty code {
  background: var(--bg3);
  padding: 2px 6px;
  border-radius: 4px;
  font-family: var(--font-mono);
  color: var(--cyan);
}
.viz-examples {
  margin-top: 24px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 8px;
}
.viz-example-btn {
  background: var(--bg2);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 8px 16px;
  color: var(--cyan);
  font-family: var(--font-mono);
  font-size: 13px;
  cursor: pointer;
  transition: all 0.15s;
  max-width: 500px;
  width: 100%;
}
.viz-example-btn:hover {
  background: var(--bg3);
  border-color: var(--accent);
  color: var(--accent);
}

/* Pipe Steps */
.viz-steps {
  width: 100%;
}
.viz-step {
  position: relative;
  margin-bottom: 4px;
}
.viz-step-header {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 6px 0 4px;
}
.viz-step-num {
  width: 28px;
  height: 28px;
  border-radius: 50%;
  background: var(--accent);
  color: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 12px;
  flex-shrink: 0;
}
.viz-step-num.error { background: var(--red); }
.viz-step-num.first { background: var(--green); }
.viz-step-fragment {
  font-family: var(--font-mono);
  font-size: 14px;
  color: var(--cyan);
  font-weight: 600;
  background: var(--bg2);
  padding: 3px 10px;
  border-radius: 6px;
  border: 1px solid var(--border);
}
.viz-step-full {
  font-family: var(--font-mono);
  font-size: 11px;
  color: var(--fg-dim);
  margin-left: auto;
  opacity: 0.6;
}
.viz-step-output {
  margin-left: 38px;
  background: var(--bg2);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 8px 12px;
  font-family: var(--font-mono);
  font-size: 12px;
  max-height: 120px;
  overflow: auto;
  white-space: pre-wrap;
  word-break: break-word;
  position: relative;
  line-height: 1.4;
  min-width: 0;
}
.viz-step-output.error {
  border-color: var(--red);
  color: var(--red);
  background: rgba(247, 118, 142, 0.05);
}
.viz-step-output.final {
  border-color: var(--green);
  background: rgba(158, 206, 106, 0.05);
}
.viz-step-type {
  position: absolute;
  top: 4px;
  right: 8px;
  font-size: 9px;
  padding: 1px 5px;
  border-radius: 3px;
  background: var(--bg3);
  color: var(--fg-dim);
}
.viz-arrow {
  margin-left: 13px;
  width: 2px;
  height: 14px;
  background: var(--border);
  position: relative;
}
.viz-arrow::after {
  content: '▼';
  position: absolute;
  bottom: -6px;
  left: -5px;
  font-size: 8px;
  color: var(--border);
}
.viz-input-step {
  margin-left: 38px;
  background: var(--bg3);
  border: 1px dashed var(--border);
  border-radius: var(--radius);
  padding: 8px 12px;
  font-family: var(--font-mono);
  font-size: 12px;
  max-height: 100px;
  overflow: auto;
  white-space: pre-wrap;
  color: var(--fg-dim);
  line-height: 1.4;
}
.viz-step-meta {
  margin-left: 38px;
  display: flex;
  gap: 12px;
  font-size: 10px;
  color: var(--fg-dim);
  padding: 2px 0;
}
/* Pipeline stretches full width */
.viz-step-meta .output-count { color: var(--yellow); }
.viz-step-meta .output-type { color: var(--accent2); }

/* Step animations */
.viz-step {
  animation: vizFadeIn 0.3s ease both;
}
.viz-step:nth-child(1) { animation-delay: 0s; }
.viz-step:nth-child(2) { animation-delay: 0.05s; }
.viz-step:nth-child(3) { animation-delay: 0.1s; }
.viz-step:nth-child(4) { animation-delay: 0.15s; }
.viz-step:nth-child(5) { animation-delay: 0.2s; }
.viz-step:nth-child(6) { animation-delay: 0.25s; }
.viz-step:nth-child(7) { animation-delay: 0.3s; }
.viz-step:nth-child(8) { animation-delay: 0.35s; }

@keyframes vizFadeIn {
  from { opacity: 0; transform: translateY(8px); }
  to { opacity: 1; transform: translateY(0); }
}

/* === EXPLAINER === */
.explain-layout {
  display: flex;
  flex-direction: column;
  height: 100%;
  width: 100%;
}
.explain-input-bar {
  border-bottom: 2px solid var(--accent);
  background: var(--bg2);
}
.explain-input-bar input {
  width: 100%;
  padding: 16px 24px;
  background: var(--bg);
  border: none;
  color: var(--accent);
  font-family: var(--font-mono);
  font-size: 18px;
  font-weight: 600;
  outline: none;
}
.explain-input-bar input:focus { background: var(--bg3); }

.explain-result {
  flex: 1;
  overflow-y: auto;
  padding: 24px 48px;
  max-width: 1200px;
}
.explain-empty {
  text-align: center;
  padding: 48px 24px;
  color: var(--fg-dim);
}
.explain-empty p { margin: 8px 0; }
.explain-examples {
  margin-top: 24px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 8px;
}

/* Token bar */
.explain-bar {
  font-family: var(--font-mono);
  font-size: 20px;
  font-weight: 600;
  padding: 16px 0 20px;
  line-height: 1.6;
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  border-bottom: 1px solid var(--border);
  margin-bottom: 20px;
}
.ex-token {
  border-bottom: 3px solid transparent;
  padding: 2px 1px;
  cursor: pointer;
  transition: all 0.15s;
  border-radius: 2px;
}
.ex-token:hover {
  background: var(--bg3);
  border-bottom-style: solid;
}
.ex-space {
  white-space: pre;
}

/* Annotations */
.explain-annotations {
  display: flex;
  flex-direction: column;
  gap: 4px;
}
.ex-annotation {
  display: grid;
  grid-template-columns: 160px 1fr;
  gap: 4px 16px;
  padding: 6px 12px;
  border-radius: var(--radius);
  border: 1px solid transparent;
  transition: all 0.15s;
  align-items: baseline;
}
.ex-annotation:hover,
.ex-annotation.highlight {
  background: var(--bg2);
  border-color: var(--border);
}
.ex-ann-header {
  display: flex;
  align-items: baseline;
  gap: 8px;
}
.ex-ann-token {
  font-family: var(--font-mono);
  font-size: 14px;
  font-weight: 700;
}
.ex-ann-cat {
  font-size: 9px;
  padding: 1px 5px;
  border-radius: 6px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}
.ex-ann-desc {
  font-size: 13px;
  color: var(--fg);
}
.ex-ann-doc {
  grid-column: 2;
  font-size: 11px;
  color: var(--fg-dim);
  font-family: var(--font-mono);
}

/* Responsive */
@media (max-width: 768px) {
  .explain-bar { font-size: 16px; }
  .ex-ann-header { min-width: 120px; }
  .ex-annotation { flex-wrap: wrap; gap: 4px; }
  .explain-input-bar input { font-size: 14px; padding: 12px 16px; }
}

/* === SHARE & TOAST === */
.share-btn {
  color: var(--accent) !important;
  cursor: pointer;
}
.share-btn:hover { background: var(--accent) !important; color: #fff !important; }
.explain-share {
  position: absolute;
  right: 12px;
  top: 50%;
  transform: translateY(-50%);
}
.explain-input-bar { position: relative; }

#share-toast {
  position: fixed;
  bottom: 24px;
  left: 50%;
  transform: translateX(-50%) translateY(100px);
  background: var(--green);
  color: #1a1b26;
  padding: 10px 24px;
  border-radius: 8px;
  font-weight: 600;
  font-size: 14px;
  opacity: 0;
  transition: all 0.3s ease;
  z-index: 1000;
  pointer-events: none;
}
#share-toast.show {
  opacity: 1;
  transform: translateX(-50%) translateY(0);
}

/* === PROGRESS BAR === */
.progress-bar-container {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 8px 12px;
  border-bottom: 1px solid var(--border);
}
.progress-bar {
  flex: 1;
  height: 4px;
  background: var(--bg3);
  border-radius: 2px;
  overflow: hidden;
}
.progress-bar-fill {
  height: 100%;
  background: var(--green);
  border-radius: 2px;
  transition: width 0.3s ease;
}
.progress-label {
  font-size: 11px;
  color: var(--fg-dim);
  white-space: nowrap;
}

/* === REFERENCE === */
.reference-layout {
  padding: 32px 48px;
  overflow-y: auto;
  height: 100%;
  width: 100%;
}
.ref-section { margin-bottom: 32px; }
.ref-section h2 {
  color: var(--accent);
  border-bottom: 2px solid var(--border);
  padding-bottom: 8px;
  margin-bottom: 16px;
}
.ref-items {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: 8px;
}
.ref-item {
  padding: 12px;
  background: var(--bg2);
  border-radius: var(--radius);
  border: 1px solid var(--border);
}
.ref-item code {
  font-family: var(--font-mono);
  color: var(--cyan);
  background: var(--bg3);
  padding: 2px 6px;
  border-radius: 3px;
}
.ref-item .ref-desc { color: var(--fg-dim); font-size: 13px; margin-top: 4px; }
.ref-item .ref-example {
  background: var(--bg3);
  padding: 8px 12px;
  margin-top: 8px;
  border-radius: 4px;
  font-family: var(--font-mono);
  font-size: 13px;
}

/* === SCROLLBAR === */
::-webkit-scrollbar { width: 8px; height: 8px; }
::-webkit-scrollbar-track { background: var(--bg); }
::-webkit-scrollbar-thumb { background: var(--bg3); border-radius: 4px; }
::-webkit-scrollbar-thumb:hover { background: var(--border); }

/* === TABLET/SMALL LAPTOP === */
@media (max-width: 1200px) {
  #lesson-sidebar, #challenge-sidebar {
    width: 240px;
    min-width: 240px;
  }
  #lesson-content, #challenge-content {
    padding: 20px 24px;
  }
  .reference-layout {
    padding: 24px;
  }
  .viz-layout {
    grid-template-columns: 200px 1fr;
  }
  .viz-filter-section input {
    font-size: 15px;
    padding: 10px 14px;
  }
  .viz-step-output, .viz-input-step {
    max-height: 100px;
    font-size: 11px;
  }
}

/* === MOBILE === */

/* Hamburger / sidebar toggle */
.sidebar-toggle {
  display: none;
  background: var(--bg3);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  color: var(--fg);
  padding: 6px 12px;
  font-size: 16px;
  cursor: pointer;
  position: fixed;
  bottom: 16px;
  left: 16px;
  z-index: 100;
  box-shadow: var(--shadow);
}

@media (max-width: 768px) {
  /* Nav */
  #topnav {
    padding: 0 10px;
    gap: 8px;
    height: 44px;
    overflow-x: auto;
    overflow-y: hidden;
    -webkit-overflow-scrolling: touch;
  }
  .nav-brand { display: none; }
  .nav-tabs { gap: 2px; flex-shrink: 0; }
  .nav-tab {
    padding: 6px 10px;
    font-size: 12px;
    white-space: nowrap;
  }
  .nav-right { gap: 8px; }
  #progress-badge { font-size: 11px; padding: 3px 8px; }

  /* Mode panels full height */
  .mode-panel { height: calc(100vh - 44px); }

  /* LEARN: sidebar as overlay */
  #mode-learn { flex-direction: column; position: relative; }
  #lesson-sidebar {
    position: fixed;
    left: 0;
    top: 44px;
    bottom: 0;
    width: 280px;
    z-index: 90;
    transform: translateX(-100%);
    transition: transform 0.25s ease;
    box-shadow: 4px 0 16px rgba(0,0,0,0.3);
  }
  #lesson-sidebar.open { transform: translateX(0); }
  .sidebar-toggle { display: block; }
  .sidebar-overlay {
    display: none;
    position: fixed;
    inset: 0;
    top: 44px;
    background: rgba(0,0,0,0.5);
    z-index: 89;
  }
  .sidebar-overlay.open { display: block; }

  #lesson-content {
    padding: 16px;
    width: 100%;
  }
  #lesson-title { font-size: 20px; }

  .exercise-panels {
    grid-template-columns: 1fr;
    gap: 8px;
  }
  .panel textarea { height: 100px; }
  .output-area { min-height: 60px; max-height: 150px; font-size: 12px; }

  .lesson-nav { gap: 8px; }
  .lesson-nav .btn { padding: 8px 14px; font-size: 13px; }

  /* PLAYGROUND: stack vertically */
  .playground-layout {
    grid-template-columns: 1fr;
    grid-template-rows: 1fr auto 1fr;
  }
  .pg-left textarea { min-height: 120px; }
  .pg-middle { order: -1; }
  .pg-middle input { font-size: 14px; padding: 10px 12px; }
  .pg-options { gap: 8px; font-size: 11px; }

  /* CHALLENGES: sidebar as overlay too */
  .challenges-layout { flex-direction: column; position: relative; }
  #challenge-sidebar {
    position: fixed;
    left: 0;
    top: 44px;
    bottom: 0;
    width: 280px;
    z-index: 90;
    transform: translateX(-100%);
    transition: transform 0.25s ease;
    box-shadow: 4px 0 16px rgba(0,0,0,0.3);
  }
  #challenge-sidebar.open { transform: translateX(0); }
  #challenge-content { padding: 16px; }

  /* VISUALIZER: stack */
  .viz-layout {
    grid-template-columns: 1fr;
    grid-template-rows: auto auto 1fr;
  }
  .viz-input-section {
    grid-row: auto;
    border-right: none;
    border-bottom: 1px solid var(--border);
    max-height: 120px;
  }
  .viz-input-section textarea { min-height: 60px; }
  .viz-filter-section input { font-size: 14px; padding: 10px 12px; }
  .viz-pipeline { padding: 16px; }
  .viz-step-full { display: none; }
  .viz-step-output { margin-left: 36px; font-size: 12px; padding: 8px 12px; }
  .viz-input-step { margin-left: 36px; font-size: 12px; }
  .viz-step-meta { margin-left: 36px; }
  .viz-step-num { width: 28px; height: 28px; font-size: 12px; }
  .viz-step-fragment { font-size: 13px; padding: 3px 8px; }
  .viz-arrow { margin-left: 13px; }
  .viz-example-btn { font-size: 11px; padding: 6px 10px; }
  .viz-examples { gap: 6px; }

  /* REFERENCE */
  .reference-layout { padding: 16px; }
  .ref-item { padding: 8px; }
  .ref-item code { font-size: 12px; }
  .ref-item .ref-desc { font-size: 12px; }
}

/* Small phones */
@media (max-width: 400px) {
  .nav-tab { padding: 5px 8px; font-size: 11px; }
  #lesson-content { padding: 12px; }
  #lesson-title { font-size: 18px; }
  .panel textarea, .panel input[type="text"] { font-size: 12px; padding: 8px; }
  .viz-step-fragment { font-size: 11px; }
}

/* Touch improvements */
@media (hover: none) and (pointer: coarse) {
  .lesson-item, .challenge-item { padding: 12px; min-height: 44px; }
  .btn, .btn-sm { min-height: 44px; display: inline-flex; align-items: center; }
  .nav-tab { min-height: 40px; display: inline-flex; align-items: center; }
  .viz-example-btn { min-height: 44px; }
  .hint-btn { padding: 8px; }
  input[type="text"], textarea { font-size: 16px !important; } /* Prevent iOS zoom */
}