:root {
  --c-text: rgba(0, 0, 0, 0.95);
  --c-text-muted: #615d59;
  --c-text-mute2: #a39e98;
  --c-bg: #ffffff;
  --c-bg-warm: #f6f5f4;
  --c-bg-dark: #31302e;

  --c-blue: #0075de;
  --c-blue-active: #005bab;
  --c-blue-focus: #097fe8;
  --c-badge-bg: #f2f9ff;
  --c-badge-text: #097fe8;

  --c-secondary-bg: rgba(0, 0, 0, 0.05);
  --c-whisper: rgba(0, 0, 0, 0.1);

  --c-green: #1aae39;
  --c-orange: #dd5b00;

  --shadow-card: rgba(0,0,0,0.04) 0px 4px 18px, rgba(0,0,0,0.027) 0px 2.025px 7.84688px, rgba(0,0,0,0.02) 0px 0.8px 2.925px, rgba(0,0,0,0.01) 0px 0.175px 1.04062px;
  --shadow-deep: rgba(0,0,0,0.01) 0px 1px 3px, rgba(0,0,0,0.02) 0px 3px 7px, rgba(0,0,0,0.02) 0px 7px 15px, rgba(0,0,0,0.04) 0px 14px 28px, rgba(0,0,0,0.05) 0px 23px 52px;

  --radius-btn: 4px;
  --radius-card: 12px;
  --radius-hero: 16px;
  --radius-pill: 9999px;

  --font-sans: 'Inter', -apple-system, system-ui, 'Segoe UI', Helvetica, 'Apple Color Emoji', Arial, sans-serif;

  --space-1: 4px;
  --space-2: 8px;
  --space-3: 12px;
  --space-4: 16px;
  --space-5: 24px;
  --space-6: 32px;
  --space-8: 48px;
  --space-10: 64px;
  --space-12: 96px;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  min-height: 100vh;
  font-family: var(--font-sans);
  font-feature-settings: "lnum" 1, "locl" 1;
  color: var(--c-text);
  background: var(--c-bg);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  font-size: 16px;
  line-height: 1.5;
}

#app {
  max-width: 800px;
  margin: 0 auto;
  padding: var(--space-6) var(--space-5) var(--space-10);
  min-height: 100vh;
}

.view { display: none; }
.view.active { display: block; }

/* ---- Typography ---- */

.display-hero {
  font-size: 48px;
  font-weight: 700;
  line-height: 1.0;
  letter-spacing: -1.5px;
  margin: 0 0 var(--space-3);
  color: var(--c-text);
}

@media (min-width: 768px) {
  .display-hero {
    font-size: 54px;
    letter-spacing: -1.875px;
    line-height: 1.04;
  }
}

.sub-heading {
  font-size: 22px;
  font-weight: 700;
  line-height: 1.27;
  letter-spacing: -0.25px;
  margin: 0 0 var(--space-3);
  color: var(--c-text);
}

.section-label {
  font-size: 20px;
  font-weight: 600;
  line-height: 1.4;
  letter-spacing: -0.125px;
  margin: 0;
  color: var(--c-text);
}

.caption {
  font-size: 16px;
  font-weight: 400;
  line-height: 1.5;
  color: var(--c-text);
  margin: 0 0 var(--space-4);
}

.caption.muted { color: var(--c-text-muted); }
.caption.error { color: var(--c-orange); }

/* ---- Buttons ---- */

.btn {
  appearance: none;
  border: 1px solid transparent;
  cursor: pointer;
  padding: 8px 16px;
  font-family: inherit;
  font-size: 15px;
  font-weight: 600;
  line-height: 1.33;
  border-radius: var(--radius-btn);
  transition: transform 120ms ease-out, background-color 120ms ease-out, color 120ms ease-out;
  user-select: none;
}

.btn:focus-visible {
  outline: 2px solid var(--c-blue-focus);
  outline-offset: 2px;
}

.btn-primary {
  background: var(--c-blue);
  color: #fff;
}
.btn-primary:hover { background: var(--c-blue-active); }
.btn-primary:active { transform: scale(0.96); }
.btn-primary:disabled { background: var(--c-text-mute2); cursor: not-allowed; }

.btn-secondary {
  background: var(--c-secondary-bg);
  color: var(--c-text);
}
.btn-secondary:hover { transform: scale(1.03); }
.btn-secondary:active { transform: scale(0.96); }

.btn-ghost {
  background: transparent;
  color: var(--c-text);
  padding: 8px 12px;
}
.btn-ghost:hover { text-decoration: underline; }

.icon-btn {
  appearance: none;
  background: transparent;
  border: none;
  color: var(--c-text-muted);
  padding: 6px;
  cursor: pointer;
  border-radius: var(--radius-btn);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  transition: color 120ms ease-out, background 120ms ease-out;
}
.icon-btn:hover { color: var(--c-text); background: var(--c-secondary-bg); }
.icon-btn:focus-visible { outline: 2px solid var(--c-blue-focus); outline-offset: 1px; }

/* ---- Pills ---- */

.pill {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  background: var(--c-badge-bg);
  color: var(--c-badge-text);
  border-radius: var(--radius-pill);
  padding: 4px 10px;
  font-size: 12px;
  font-weight: 600;
  letter-spacing: 0.125px;
  line-height: 1.33;
  white-space: nowrap;
}

.key-pill {
  font-family: ui-monospace, 'SF Mono', Menlo, monospace;
  font-size: 11px;
  max-width: 100%;
  overflow-x: auto;
}

/* ---- Import View ---- */

.import-card {
  max-width: 560px;
  margin: var(--space-12) auto 0;
  padding: var(--space-8);
  background: #fff;
  border: 1px solid var(--c-whisper);
  border-radius: var(--radius-hero);
  box-shadow: var(--shadow-deep);
  text-align: center;
}

.drop-zone {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--space-3);
  padding: var(--space-8) var(--space-5);
  margin-top: var(--space-5);
  border: 1px dashed var(--c-whisper);
  border-radius: var(--radius-card);
  background: #fff;
  cursor: pointer;
  transition: background 120ms ease-out, border-color 120ms ease-out;
}

.drop-zone:hover, .drop-zone.drag-over {
  background: var(--c-bg-warm);
  border-color: rgba(0, 0, 0, 0.2);
}

.drop-text {
  font-size: 16px;
  font-weight: 500;
  color: var(--c-text);
}

.drop-sep {
  font-size: 14px;
  font-weight: 400;
  color: var(--c-text-mute2);
}

.drop-btn {
  margin-top: var(--space-2);
}

/* ---- Review View ---- */

.review-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: var(--space-4);
  margin-bottom: var(--space-5);
}

.header-right {
  display: flex;
  align-items: center;
  gap: var(--space-3);
}

.banner {
  display: none;
  padding: var(--space-3) var(--space-4);
  background: #fff3ea;
  color: var(--c-orange);
  border: 1px solid var(--c-whisper);
  border-radius: var(--radius-card);
  font-size: 14px;
  line-height: 1.43;
  margin-bottom: var(--space-4);
}

.banner.active { display: block; }

.card-stage {
  perspective: 1400px;
  margin: var(--space-4) 0 var(--space-6);
  display: flex;
  justify-content: center;
  min-height: 360px;
}

.flashcard {
  width: 100%;
  max-width: 600px;
  aspect-ratio: 3 / 2;
  min-height: 360px;
  position: relative;
  transition: transform 320ms cubic-bezier(0.22, 0.61, 0.36, 1), opacity 320ms ease-out;
  touch-action: pan-y;
  will-change: transform;
  cursor: pointer;
}

.flashcard.dragging { transition: none; }
.flashcard.no-transition,
.flashcard.no-transition .card-inner { transition: none !important; }

.flashcard.exit-left  { transform: translateX(-150vw) rotate(-18deg); opacity: 0; }
.flashcard.exit-right { transform: translateX(150vw) rotate(18deg); opacity: 0; }
.flashcard.exit-up    { transform: translateY(-120vh); opacity: 0; }

.card-inner {
  position: absolute;
  inset: 0;
  transform-style: preserve-3d;
  transition: transform 320ms cubic-bezier(0.22, 0.61, 0.36, 1);
}

.flashcard.flipped .card-inner { transform: rotateY(180deg); }

.card-face {
  position: absolute;
  inset: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: var(--space-6);
  background: #fff;
  border: 1px solid var(--c-whisper);
  border-radius: var(--radius-hero);
  box-shadow: var(--shadow-deep);
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
  overflow: hidden;
}

.card-back {
  transform: rotateY(180deg);
  justify-content: flex-start;
  align-items: stretch;
  padding: var(--space-6);
  overflow-y: auto;
}

.card-word {
  font-size: 64px;
  font-weight: 700;
  line-height: 1.0;
  letter-spacing: -2.125px;
  color: var(--c-text);
  margin: 0 0 var(--space-3);
  text-align: center;
  word-break: break-word;
}

.card-word-back {
  font-size: 40px;
  letter-spacing: -1.25px;
  line-height: 1.1;
  margin-bottom: var(--space-2);
  text-align: left;
}

.card-phonetic {
  font-size: 20px;
  font-weight: 400;
  line-height: 1.4;
  color: var(--c-text-muted);
  margin: 0 0 var(--space-4);
  text-align: center;
  word-break: break-word;
}

.card-back .card-phonetic { text-align: left; margin-bottom: var(--space-4); }

.audio-row {
  display: flex;
  gap: var(--space-2);
  margin-bottom: var(--space-4);
}

.audio-pill {
  appearance: none;
  background: var(--c-badge-bg);
  color: var(--c-badge-text);
  border: none;
  border-radius: var(--radius-pill);
  padding: 6px 12px;
  font-family: inherit;
  font-size: 12px;
  font-weight: 600;
  letter-spacing: 0.125px;
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  gap: 4px;
  transition: background 120ms ease-out, transform 120ms ease-out;
}
.audio-pill:hover { background: #e6f2ff; }
.audio-pill:active { transform: scale(0.95); }
.audio-pill:focus-visible { outline: 2px solid var(--c-blue-focus); outline-offset: 2px; }

.audio-icon { font-size: 11px; }

.card-hint {
  font-size: 14px;
  font-weight: 400;
  color: var(--c-text-mute2);
  margin: 0;
}

.card-explanation {
  font-size: 16px;
  line-height: 1.6;
  color: var(--c-text);
  width: 100%;
}
.card-explanation ol, .card-explanation ul {
  margin: 0 0 var(--space-3);
  padding-left: 24px;
}
.card-explanation li { margin-bottom: 4px; }
.card-explanation i { color: var(--c-text-muted); font-style: italic; margin-right: 4px; }
.card-explanation .txtDisabled { color: var(--c-text-mute2); font-size: 13px; }
.card-explanation .trans { color: var(--c-text-muted); font-size: 13px; }
.card-explanation #trans,
.card-explanation .expDiv { display: block; }

/* ---- Action buttons ---- */

.action-row {
  display: flex;
  gap: var(--space-3);
  justify-content: center;
  flex-wrap: wrap;
  margin-bottom: var(--space-4);
}

.action-arrow {
  font-family: ui-monospace, 'SF Mono', Menlo, monospace;
  font-weight: 600;
}

.stats-line {
  text-align: center;
  font-size: 14px;
  margin: 0;
}

/* ---- Done View ---- */

.done-card {
  max-width: 560px;
  margin: var(--space-10) auto 0;
  padding: var(--space-8);
  background: var(--c-bg-warm);
  border: 1px solid var(--c-whisper);
  border-radius: var(--radius-hero);
  box-shadow: var(--shadow-card);
  text-align: center;
}

.done-icon {
  width: 64px;
  height: 64px;
  margin: 0 auto var(--space-4);
  border-radius: 50%;
  background: var(--c-green);
  color: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
}

.done-actions {
  display: flex;
  gap: var(--space-3);
  justify-content: center;
  margin-top: var(--space-5);
  flex-wrap: wrap;
}

/* ---- Settings View ---- */

.settings-body {
  display: flex;
  flex-direction: column;
  gap: var(--space-6);
  margin-top: var(--space-4);
}

.settings-section {
  background: #fff;
  border: 1px solid var(--c-whisper);
  border-radius: var(--radius-card);
  padding: var(--space-5);
  box-shadow: var(--shadow-card);
}

.settings-section.danger .btn { color: var(--c-text); }

.sync-key-row {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  margin-top: var(--space-3);
  flex-wrap: wrap;
}

.sync-paste-row {
  display: flex;
  gap: var(--space-2);
  margin-top: var(--space-3);
  flex-wrap: wrap;
}

.sync-row {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  margin-top: var(--space-3);
  flex-wrap: wrap;
}

.text-input {
  flex: 1;
  min-width: 200px;
  padding: 6px 10px;
  border: 1px solid #dddddd;
  border-radius: var(--radius-btn);
  background: #fff;
  font-family: inherit;
  font-size: 14px;
  color: var(--c-text);
}

.text-input::placeholder { color: var(--c-text-mute2); }
.text-input:focus { outline: 2px solid var(--c-blue-focus); outline-offset: 0; border-color: var(--c-blue-focus); }

.sync-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--c-text-mute2);
  display: inline-block;
}
.sync-dot.good { background: var(--c-green); }
.sync-dot.stale { background: var(--c-orange); }

.slider {
  width: 100%;
  margin: var(--space-2) 0;
  accent-color: var(--c-blue);
}

.radio-row { display: flex; gap: var(--space-4); margin-top: var(--space-2); }
.radio {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-size: 15px;
  font-weight: 500;
  cursor: pointer;
}
.radio input { accent-color: var(--c-blue); }

.stats-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(88px, 1fr));
  gap: var(--space-3);
  margin-top: var(--space-3);
}

.stat {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  gap: 2px;
  padding: var(--space-3);
  background: var(--c-bg-warm);
  border-radius: var(--radius-btn);
}

.stat-num {
  font-size: 26px;
  font-weight: 700;
  letter-spacing: -0.625px;
  line-height: 1.23;
  color: var(--c-text);
}

.stat-label {
  font-size: 12px;
  font-weight: 500;
  color: var(--c-text-muted);
}

.button-stack {
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
  align-items: flex-start;
  margin-top: var(--space-3);
}

/* ---- Responsive ---- */

@media (max-width: 600px) {
  #app { padding: var(--space-4) var(--space-3) var(--space-8); }
  .card-word { font-size: 40px; letter-spacing: -1.25px; }
  .card-word-back { font-size: 30px; letter-spacing: -0.75px; }
  .display-hero { font-size: 40px; letter-spacing: -1.25px; }
  .action-row .btn { flex: 1 1 auto; }
  .card-face { padding: var(--space-5); }
  .import-card, .done-card { padding: var(--space-5); margin-top: var(--space-6); }
}

@media (max-width: 400px) {
  .card-word { font-size: 32px; letter-spacing: -1px; }
  .card-word-back { font-size: 26px; letter-spacing: -0.625px; }
}