:root {
  --bg-app: #f7f8fb;
  --bg-panel: #ffffff;
  --bg-canvas: #ffffff;
  --text-main: #1f2937;
  --text-sub: #6b7280;
  --accent: #3b82f6;
  --btn-bg: #eef2f7;
  --btn-hover: #e3eaf5;
  --btn-correct: #dff4df;
  --btn-wrong: #f7dddd;
  --border: #d6dbe6;

  --page-max: 980px;
  --canvas-ratio: 760 / 460;
}

* {
  box-sizing: border-box;
}

html {
  min-width: 0;
  background: var(--bg-app);
  -webkit-text-size-adjust: 100%;
}

body {
  margin: 0;
  min-width: 0;
  overflow-x: hidden;
  background: var(--bg-app);
  color: var(--text-main);
  font-family: "Segoe UI", system-ui, -apple-system, BlinkMacSystemFont, sans-serif;
}

button,
input {
  font: inherit;
}

button {
  -webkit-tap-highlight-color: transparent;
}

.app {
  width: min(var(--page-max), 100%);
  min-height: 100dvh;
  margin: 0 auto;
  padding: max(12px, env(safe-area-inset-top)) max(12px, env(safe-area-inset-right))
           max(16px, env(safe-area-inset-bottom)) max(12px, env(safe-area-inset-left));
}

.header h1 {
  margin: 0;
  font-size: clamp(22px, 5.6vw, 24px);
  line-height: 1.2;
  letter-spacing: -0.02em;
}

.header p {
  margin: 6px 0 14px;
  color: var(--text-sub);
  font-size: clamp(12px, 3.3vw, 13px);
  line-height: 1.45;
}

.card {
  width: 100%;
  background: var(--bg-panel);
  border-radius: 14px;
  padding: clamp(12px, 3.5vw, 16px);
  box-shadow: 0 10px 30px rgba(15, 23, 42, 0.06);
}

.top-bar {
  display: flex;
  justify-content: space-between;
  gap: 18px;
  align-items: flex-start;
  margin-bottom: 12px;
}

.settings-panel {
  flex: 1;
  min-width: 0;
}

.settings-panel summary {
  min-height: 42px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: 9px 12px;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: #fbfcff;
  color: var(--text-main);
  font-size: 14px;
  font-weight: 700;
  cursor: pointer;
  user-select: none;
  list-style: none;
}

.settings-panel summary::-webkit-details-marker {
  display: none;
}

.settings-panel summary::after {
  content: "▾";
  color: var(--text-sub);
  font-size: 14px;
  transition: transform 160ms ease;
}

.settings-panel[open] summary::after {
  transform: rotate(180deg);
}

.settings-summary {
  margin-left: auto;
  overflow: hidden;
  color: var(--text-sub);
  font-size: 12px;
  font-weight: 500;
  text-align: right;
  white-space: nowrap;
  text-overflow: ellipsis;
}

.settings-panel .controls {
  margin-top: 10px;
}

.controls {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 9px 14px;
  font-size: 13px;
  line-height: 1.35;
}

.controls label {
  display: flex;
  align-items: flex-start;
  gap: 7px;
  user-select: none;
  cursor: pointer;
  min-height: 24px;
}

.controls input {
  flex: 0 0 auto;
  width: 16px;
  height: 16px;
  margin: 1px 0 0;
}

.controls label.disabled {
  color: #a3aab8;
  cursor: not-allowed;
}

.controls label.disabled input {
  cursor: not-allowed;
}

.info {
  min-width: 245px;
  text-align: right;
  color: var(--text-sub);
  font-size: 12px;
  line-height: 1.45;
}

#timerLabel {
  margin-top: 3px;
  color: var(--accent);
  font-size: 14px;
  font-weight: 700;
}

#scoreLabel {
  margin-top: 3px;
}

h2 {
  margin: 4px 0 8px;
  font-size: 14px;
}

.canvas-frame {
  width: 100%;
  margin: 0 auto;
  border: 1px solid var(--border);
  background: var(--border);
  overflow: hidden;
  border-radius: 4px;
  touch-action: none;
}

canvas {
  display: block;
  width: 100%;
  height: auto;
  aspect-ratio: var(--canvas-ratio);
  background: var(--bg-canvas);
  cursor: default;
  touch-action: none;
}

canvas.draw-mode {
  cursor: crosshair;
}

.question {
  min-height: 46px;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 14px 6px 10px;
  font-size: clamp(14px, 3.8vw, 16px);
  font-weight: 700;
  line-height: 1.38;
  text-align: center;
}

.options {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 14px;
}

.option {
  min-height: 56px;
  border: 0;
  border-radius: 10px;
  background: var(--btn-bg);
  color: var(--text-main);
  font-size: clamp(15px, 4.2vw, 17px);
  font-weight: 700;
  cursor: pointer;
  touch-action: manipulation;
}

.option:hover:not(:disabled) {
  background: var(--btn-hover);
}

.option.correct {
  background: var(--btn-correct);
}

.option.wrong {
  background: var(--btn-wrong);
}

.option:disabled {
  cursor: default;
  opacity: 1;
}

.bottom-bar {
  display: flex;
  align-items: center;
  gap: 14px;
  margin-top: 16px;
}

.feedback {
  flex: 1;
  min-height: 38px;
  font-size: 13px;
  line-height: 1.5;
}

.nav {
  display: flex;
  gap: 8px;
}

.nav-btn {
  min-height: 42px;
  border: 1px solid var(--border);
  border-radius: 9px;
  padding: 9px 15px;
  background: #fff;
  color: var(--text-main);
  font-size: 13px;
  font-weight: 700;
  cursor: pointer;
  touch-action: manipulation;
}

.nav-btn:hover:not(:disabled) {
  background: var(--btn-hover);
}

.nav-btn:disabled {
  color: #a3aab8;
  cursor: default;
}

/* Tablet and narrow desktop */
@media (max-width: 840px) {
  .top-bar {
    flex-direction: column;
    gap: 12px;
  }

  .settings-panel {
    width: 100%;
  }

  .controls {
    width: 100%;
    grid-template-columns: 1fr;
    gap: 10px;
    font-size: 14px;
  }

  .info {
    min-width: 0;
    width: 100%;
    text-align: left;
    font-size: 12px;
    padding-top: 2px;
    border-top: 1px solid #eef2f7;
  }

  .options {
    gap: 10px;
  }
}

/* Phone */
@media (max-width: 600px) {
  .app {
    padding-left: max(10px, env(safe-area-inset-left));
    padding-right: max(10px, env(safe-area-inset-right));
  }

  .header h1 {
    font-size: 22px;
  }

  .header p {
    margin-bottom: 10px;
  }

  .card {
    border-radius: 12px;
    padding: 10px;
  }

  h2 {
    font-size: 13px;
  }

  .canvas-frame {
    width: 100%;
    border-radius: 6px;
  }

  .question {
    min-height: auto;
    padding: 12px 4px 9px;
    font-size: 15px;
  }

  .options {
    grid-template-columns: 1fr;
    gap: 9px;
  }

  .option {
    min-height: 50px;
    border-radius: 10px;
    font-size: 16px;
  }

  .bottom-bar {
    flex-direction: column;
    align-items: stretch;
    gap: 10px;
    margin-top: 12px;
  }

  .feedback {
    min-height: 0;
    font-size: 13px;
  }

  .nav {
    width: 100%;
    display: grid;
    grid-template-columns: 1fr 1fr;
  }

  .nav-btn {
    width: 100%;
    min-height: 44px;
    font-size: 14px;
  }
}

/* Very small phones */
@media (max-width: 380px) {
  .app {
    padding-left: 8px;
    padding-right: 8px;
  }

  .card {
    padding: 8px;
  }

  .controls {
    font-size: 13px;
    gap: 8px;
  }

  .question {
    font-size: 14px;
  }

  .option {
    min-height: 48px;
    font-size: 15px;
  }
}

/* Landscape phones: keep the training area compact. */
@media (max-height: 520px) and (orientation: landscape) {
  .app {
    padding-top: 8px;
    padding-bottom: 8px;
  }

  .header {
    display: none;
  }

  .top-bar {
    margin-bottom: 8px;
  }

  .controls {
    grid-template-columns: 1fr 1fr;
    font-size: 12px;
    gap: 6px 10px;
  }

  .info {
    display: grid;
    grid-template-columns: 1fr auto auto;
    gap: 10px;
    align-items: center;
  }

  #timerLabel,
  #scoreLabel {
    margin-top: 0;
  }

  .question {
    padding: 8px 4px 6px;
  }

  .option {
    min-height: 42px;
  }

  .bottom-bar {
    margin-top: 8px;
  }
}

#modeLabel { display: none !important; }


.info {
  min-width: 190px;
}

@media (max-width: 840px) {
  .info {
    padding-top: 8px;
  }
}



.title-row {
  display: flex;
  align-items: center;
  gap: 8px;
}

.help-btn {
  width: 22px;
  height: 22px;
  border: 1px solid var(--border);
  border-radius: 999px;
  background: #fff;
  color: var(--text-sub);
  font-size: 13px;
  font-weight: 800;
  line-height: 1;
  cursor: pointer;
  touch-action: manipulation;
}

.help-btn:hover {
  background: var(--btn-hover);
  color: var(--text-main);
}

.help-modal[hidden] {
  display: none;
}

.help-modal {
  position: fixed;
  inset: 0;
  z-index: 1000;
  padding: max(16px, env(safe-area-inset-top)) max(12px, env(safe-area-inset-right))
           max(16px, env(safe-area-inset-bottom)) max(12px, env(safe-area-inset-left));
  display: grid;
  place-items: center;
}

.help-backdrop {
  position: absolute;
  inset: 0;
  background: rgba(15, 23, 42, 0.42);
  backdrop-filter: blur(2px);
}

.help-dialog {
  position: relative;
  width: min(720px, 100%);
  max-height: min(78dvh, 720px);
  display: flex;
  flex-direction: column;
  overflow: hidden;
  border-radius: 16px;
  background: #fff;
  box-shadow: 0 24px 80px rgba(15, 23, 42, 0.28);
}

.help-dialog-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding: 14px 16px;
  border-bottom: 1px solid var(--border);
}

.help-dialog-header h2 {
  margin: 0;
  font-size: 18px;
}

.help-close-btn {
  width: 32px;
  height: 32px;
  border: 0;
  border-radius: 999px;
  background: var(--btn-bg);
  color: var(--text-main);
  font-size: 22px;
  line-height: 1;
  cursor: pointer;
}

.help-close-btn:hover {
  background: var(--btn-hover);
}

.help-content {
  overflow: auto;
  padding: 16px 18px 20px;
  color: var(--text-main);
  font-size: 14px;
  line-height: 1.65;
}

.markdown-body h3 {
  margin: 18px 0 8px;
  font-size: 16px;
}

.markdown-body h4 {
  margin: 14px 0 6px;
  font-size: 14px;
}

.markdown-body p {
  margin: 8px 0;
}

.markdown-body ul,
.markdown-body ol {
  margin: 8px 0 8px 22px;
  padding: 0;
}

.markdown-body li {
  margin: 4px 0;
}

.markdown-body code {
  padding: 1px 4px;
  border-radius: 4px;
  background: #f1f5f9;
  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  font-size: 0.92em;
}

.markdown-body hr {
  border: 0;
  border-top: 1px solid var(--border);
  margin: 14px 0;
}

@media (max-width: 600px) {
  .help-btn {
    width: 24px;
    height: 24px;
  }

  .help-modal {
    align-items: end;
    padding: 8px;
  }

  .help-dialog {
    width: 100%;
    max-height: 86dvh;
    border-radius: 16px 16px 10px 10px;
  }

  .help-dialog-header {
    padding: 12px 14px;
  }

  .help-content {
    padding: 14px;
    font-size: 13px;
  }
}



/* Layout fixes: compact title, aligned top row, full-width canvas. */
.header {
  margin-bottom: 14px;
}

.title-row {
  align-items: flex-start;
}

.help-btn {
  width: 16px;
  height: 16px;
  margin-top: 1px;
  padding: 0;
  font-size: 10px;
  line-height: 14px;
  transform: translateY(-1px);
}

.top-bar {
  align-items: center;
}

.info {
  min-height: 42px;
  display: flex;
  flex-direction: column;
  justify-content: center;
}

.canvas-frame {
  width: 100%;
  max-width: none;
}

.options {
  width: 100%;
}

@media (max-width: 840px) {
  .top-bar {
    align-items: stretch;
  }

  .info {
    min-height: auto;
    display: block;
  }
}



.math-block {
  overflow-x: auto;
  padding: 2px 0;
}



.difficulty-panel {
  min-height: 42px;
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 0 2px;
  white-space: nowrap;
}

.difficulty-panel label {
  color: var(--text-sub);
  font-size: 12px;
  font-weight: 700;
}

.difficulty-panel select {
  min-height: 38px;
  padding: 0 30px 0 10px;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: #fff;
  color: var(--text-main);
  font-size: 13px;
  font-weight: 700;
  cursor: pointer;
}

.help-frame {
  display: block;
  width: 100%;
  height: min(68dvh, 620px);
  border: 0;
  background: #fff;
}

@media (max-width: 840px) {
  .difficulty-panel {
    width: 100%;
    justify-content: space-between;
    padding: 0;
  }

  .difficulty-panel select {
    flex: 0 0 150px;
  }
}

@media (max-width: 600px) {
  .difficulty-panel select {
    flex-basis: 140px;
  }

  .help-frame {
    height: 72dvh;
  }
}



.cookbook-btn {
  min-height: 24px;
  padding: 3px 8px;
  border: 1px solid var(--border);
  border-radius: 999px;
  background: #fff;
  color: var(--text-sub);
  font-size: 11px;
  font-weight: 800;
  line-height: 1;
  cursor: pointer;
  touch-action: manipulation;
  transform: translateY(-2px);
}

.cookbook-btn:hover {
  background: var(--btn-hover);
  color: var(--text-main);
}

.tutorial-dialog {
  width: min(860px, 100%);
}

@media (max-width: 600px) {
  .cookbook-btn {
    min-height: 22px;
    padding: 3px 7px;
    font-size: 10px;
  }

  .title-row {
    flex-wrap: wrap;
  }
}