:root {
  color-scheme: light;
  font-family: Inter, "PingFang SC", "Microsoft YaHei", sans-serif;
  color: #20213c;
  background: #f7f8fc;
  --brand: #5b5ce2;
  --brand-soft: #eeeffe;
  --muted: #7778a9;
  --line: #e5e5f3;
  --known: #16805c;
  --known-soft: #e8fbf2;
  --again: #b43b55;
  --again-soft: #fff0f0;
  --hard: #9a6a0a;
  --hard-soft: #fff8e5;
  --card-radius: 24px;
  --shadow-card: 0 16px 44px rgba(49, 48, 105, 0.09);
  --ease: cubic-bezier(0.22, 0.8, 0.24, 1);
}
* { box-sizing: border-box; }
html, body { overflow-x: hidden; overscroll-behavior-x: none; }
body {
  margin: 0;
  min-width: 320px;
  min-height: 100vh;
  min-height: 100dvh;
  background:
    radial-gradient(920px 480px at 50% -12%, rgba(91, 92, 226, 0.075), transparent 62%),
    #f7f8fc;
}
button, input, select { font: inherit; color: inherit; }
button { cursor: pointer; }
button:focus-visible, select:focus-visible, .word-card:focus-visible {
  outline: 2px solid var(--brand);
  outline-offset: 2px;
}
h1, h2, p { margin: 0; }

.app {
  display: flex;
  flex-direction: column;
  width: min(100%, 680px);
  min-height: 100vh;
  min-height: 100dvh;
  margin: 0 auto;
  padding: 28px 20px max(24px, env(safe-area-inset-bottom));
}
.topbar {
  display: flex;
  flex: none;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}
h1 { font-size: 1.5rem; letter-spacing: -0.04em; }
.eyebrow {
  margin-bottom: 4px;
  color: #686a99;
  font-size: 0.68rem;
  font-weight: 800;
  letter-spacing: 0.12em;
}
.icon-button {
  border: 0;
  border-radius: 12px;
  padding: 10px 12px;
  background: var(--brand-soft);
  color: #4748c7;
}

.progress-region { flex: none; margin: 24px 0 16px; }
.progress-copy {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 8px;
  color: #6d6e8f;
  font-size: 0.85rem;
}
.progress-slider {
  padding: 9px 0;
  border-radius: 8px;
  cursor: pointer;
  touch-action: none;
  user-select: none;
  -webkit-user-select: none;
}
.progress-slider.is-dragging { cursor: grabbing; }
.progress-slider:focus-visible { outline: 2px solid var(--brand); outline-offset: 4px; }
.progress-track { position: relative; height: 7px; border-radius: 8px; background: #e5e6f4; }
.progress-track i {
  display: block;
  width: 0;
  height: 100%;
  border-radius: inherit;
  background: linear-gradient(90deg, #7879f5, #4bc6d8);
  transition: width 0.25s var(--ease);
  pointer-events: none;
}
.progress-thumb {
  position: absolute;
  z-index: 1;
  top: 50%;
  left: var(--progress, 0%);
  width: 14px;
  height: 14px;
  border: 2px solid var(--brand);
  border-radius: 50%;
  background: #fff;
  box-shadow: 0 2px 8px rgba(49, 48, 105, 0.18);
  transform: translate(-50%, -50%);
  transition: left 0.25s var(--ease), transform 0.15s ease, box-shadow 0.15s ease;
  pointer-events: none;
}
.progress-slider:hover .progress-thumb,
.progress-slider:focus-visible .progress-thumb { transform: translate(-50%, -50%) scale(1.1); }
.progress-slider.is-dragging .progress-thumb {
  transform: translate(-50%, -50%) scale(1.18);
  transition: transform 0.15s ease, box-shadow 0.15s ease;
}
.progress-slider.is-dragging .progress-track i { transition: none; }

/* Deck picker: a custom box trigger and a custom listbox, no native select. */
.deck-picker { position: relative; flex: none; margin: 0 0 16px; }
.deck-box {
  display: flex;
  width: 100%;
  align-items: center;
  gap: 12px;
  padding: 10px 14px;
  border: 1px solid var(--line);
  border-radius: 16px;
  background: #fff;
  box-shadow: 0 4px 16px rgba(49, 48, 105, 0.045);
  text-align: left;
  transition: border-color 0.16s ease, box-shadow 0.16s ease;
}
.deck-box:hover { border-color: #d6d7f0; }
.deck-box:focus-visible {
  border-color: #b9baf4;
  outline: none;
  box-shadow: 0 0 0 3px rgba(91, 92, 226, 0.1);
}
.deck-box-icon {
  display: grid;
  flex: none;
  place-items: center;
  width: 36px;
  height: 36px;
  border-radius: 11px;
  background: var(--brand-soft);
  color: #4748c7;
  font-size: 0.78rem;
  font-weight: 800;
  letter-spacing: -0.02em;
}
.deck-box-body { display: flex; flex: 1; flex-direction: column; gap: 1px; min-width: 0; }
.deck-box-caption { color: #8a8ba8; font-size: 0.66rem; font-weight: 750; letter-spacing: 0.08em; }
.deck-box-value {
  overflow: hidden;
  color: #3d3e62;
  font-size: 0.92rem;
  font-weight: 750;
  line-height: 1.4;
  text-overflow: ellipsis;
  white-space: nowrap;
}
.deck-arrow {
  display: grid;
  flex: none;
  place-items: center;
  width: 30px;
  height: 30px;
  border-radius: 10px;
  background: #f4f5fb;
  color: #8a8ba8;
  transition: transform 0.2s var(--ease), background-color 0.2s ease, color 0.2s ease;
}
.deck-picker.is-open .deck-arrow { transform: rotate(180deg); background: var(--brand-soft); color: var(--brand); }
.deck-menu {
  position: absolute;
  z-index: 30;
  top: calc(100% + 8px);
  right: 0;
  left: 0;
  padding: 6px;
  border: 1px solid var(--line);
  border-radius: 16px;
  background: #fff;
  box-shadow: 0 20px 50px rgba(49, 48, 105, 0.18);
  animation: deckMenuIn 0.16s var(--ease);
}
.deck-menu[hidden] { display: none; }
@keyframes deckMenuIn {
  from { opacity: 0; transform: translateY(-4px) scale(0.99); }
  to { opacity: 1; transform: none; }
}
.deck-option {
  display: flex;
  width: 100%;
  align-items: center;
  gap: 10px;
  padding: 10px 12px;
  border: 0;
  border-radius: 11px;
  background: transparent;
  color: #3d3e62;
  text-align: left;
  font-size: 0.86rem;
  font-weight: 650;
}
.deck-option + .deck-option { margin-top: 2px; }
.deck-option:hover, .deck-option:focus-visible { background: #f5f6fc; outline: none; }
.deck-option[aria-selected="true"] { background: var(--brand-soft); color: #4748c7; }
.deck-option-label { flex: 1; min-width: 0; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.deck-option-count { color: #8a8ba8; font-size: 0.72rem; font-variant-numeric: tabular-nums; }
.deck-option[aria-selected="true"] .deck-option-count { color: #6364d9; }
.deck-option-check { width: 16px; color: var(--brand); text-align: center; font-weight: 800; opacity: 0; }
.deck-option[aria-selected="true"] .deck-option-check { opacity: 1; }

/* Card stage: fills the remaining height; the card is the fixed shell. */
.card-stage {
  position: relative;
  display: flex;
  flex: 1 1 auto;
  min-height: 320px;
  max-height: 760px;
  border-radius: var(--card-radius);
}
.swipe-hint {
  position: absolute;
  inset: 0;
  z-index: 0;
  display: flex;
  flex-direction: column;
  justify-content: center;
  gap: 2px;
  padding: 0 30px;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: var(--card-radius);
  opacity: 0;
  pointer-events: none;
}
.hint-known {
  align-items: flex-end;
  text-align: right;
  background: linear-gradient(100deg, #fff 12%, var(--known-soft) 100%);
}
.hint-unknown {
  align-items: flex-start;
  text-align: left;
  background: linear-gradient(260deg, #fff 12%, var(--again-soft) 100%);
}
.hint-direction { color: #8a8ba8; font-size: 0.7rem; font-weight: 700; letter-spacing: 0.04em; }
.hint-verdict { font-size: 1.15rem; font-weight: 800; letter-spacing: 0.02em; line-height: 1.3; }
.hint-known .hint-verdict { color: var(--known); }
.hint-unknown .hint-verdict { color: var(--again); }
.hint-sub { color: #8a8ba8; font-size: 0.7rem; }
.card-preview {
  position: absolute;
  inset: 0;
  z-index: 1;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 18px 20px 70px;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: var(--card-radius);
  background: #fff;
  box-shadow: var(--shadow-card);
  opacity: 0;
  pointer-events: none;
}
.card-preview.is-visible { animation: previewIn 0.26s linear both; }
@keyframes previewIn {
  from { opacity: 0; transform: scale(0.985); }
  to { opacity: 1; transform: scale(1); }
}
.preview-tag {
  position: absolute;
  top: 18px;
  left: 20px;
  padding: 3px 9px;
  border-radius: 999px;
  background: var(--brand-soft);
  color: #4748c7;
  font-size: 0.7rem;
  font-weight: 750;
  line-height: 1.2;
  letter-spacing: 0.02em;
}
.preview-word {
  max-width: 100%;
  color: #20213c;
  font-size: clamp(2.2rem, 10.5vw, 4rem);
  font-weight: 800;
  letter-spacing: -0.055em;
  line-height: 1.04;
  overflow-wrap: anywhere;
  text-align: center;
}

.word-card {
  position: relative;
  z-index: 2;
  display: flex;
  flex: 1 1 auto;
  flex-direction: column;
  min-width: 0;
  min-height: 0;
  padding: 18px 20px 16px;
  border: 1px solid var(--line);
  border-radius: var(--card-radius);
  outline: none;
  background: #fff;
  box-shadow: var(--shadow-card);
  cursor: pointer;
  touch-action: pan-y;
  user-select: none;
  -webkit-user-select: none;
  -webkit-tap-highlight-color: transparent;
  transform: translate3d(0, 0, 0);
  transition: transform 0.5s var(--ease), opacity 0.48s var(--ease), border-color 0.18s ease;
  will-change: transform;
}
.word-card.is-dragging { cursor: grabbing; transition: none; }
.word-card.is-leaving {
  transform: translate3d(calc(var(--dir, 1) * 130%), 0, 0) rotate(calc(var(--dir, 1) * 5deg)) scale(0.9);
  opacity: 0;
  transition: transform 0.465s ease-in-out, opacity 0.465s ease-in-out;
}
.word-card.is-resetting { transition: none !important; }
.word-card.swipe-ok { border-color: var(--known); }
.word-card.swipe-bad { border-color: var(--again); }
.word-card::after {
  content: "";
  position: absolute;
  right: 1px;
  bottom: 1px;
  left: 1px;
  height: 52%;
  border-radius: 0 0 calc(var(--card-radius) - 1px) calc(var(--card-radius) - 1px);
  background: radial-gradient(ellipse at 50% 100%, rgba(91, 92, 226, 0.085), transparent 68%);
  pointer-events: none;
}
.card-head, .card-viewport, .card-foot { position: relative; z-index: 1; }

.card-head {
  display: flex;
  flex: none;
  align-items: flex-start;
  justify-content: space-between;
  gap: 12px;
  min-height: 30px;
}
.tags { display: flex; flex-wrap: wrap; align-items: center; gap: 6px; min-width: 0; min-height: 24px; }
.tag {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  min-height: 24px;
  padding: 3px 9px;
  border-radius: 999px;
  font-size: 0.7rem;
  font-weight: 750;
  line-height: 1.2;
  white-space: nowrap;
}
.tag--priority { color: #4748c7; background: var(--brand-soft); }
.tag--priority::before {
  content: "";
  width: 5px;
  height: 5px;
  border-radius: 50%;
  background: currentColor;
  opacity: 0.75;
}
.tag--priority[data-level="S"] {
  color: #fff;
  background: linear-gradient(135deg, #6d6ef2, #5b5ce2);
  box-shadow: 0 4px 10px rgba(91, 92, 226, 0.24);
}
.tag--priority[data-level="A"] { color: #4748c7; background: #e9e9ff; }
.tag--priority[data-level="B"] { color: var(--hard); background: var(--hard-soft); }
.tag--priority[data-level="C"] { color: #686a99; background: #f1f2f9; }
.tag--source { color: #686a99; background: #f4f5fb; }
.tag--known { color: var(--known); background: var(--known-soft); }
.tag--known::before { content: "✓"; font-size: 0.66rem; }
.tag--learning { color: var(--hard); background: var(--hard-soft); }
.tag--again { color: var(--again); background: var(--again-soft); }
.speak {
  flex: none;
  border: 0;
  border-radius: 12px;
  padding: 9px 12px;
  background: var(--brand-soft);
  color: #4748c7;
  font-size: 0.8rem;
  font-weight: 700;
  transition: background-color 0.16s ease, transform 0.12s ease;
}
.speak:active { transform: scale(0.97); }

.card-viewport {
  position: relative;
  flex: 1 1 auto;
  min-height: 0;
  perspective: 1600px;
}
.card-inner {
  position: absolute;
  inset: 0;
  display: grid;
  grid-template-areas: "face";
  grid-template-rows: minmax(0, 1fr);
  border-radius: 18px;
  transform-style: preserve-3d;
  transition: transform 0.52s var(--ease);
}
.card-inner.is-revealed { transform: rotateY(180deg); }
.card-inner.is-resetting { transition: none !important; }
.card-face {
  grid-area: face;
  display: flex;
  flex-direction: column;
  min-width: 0;
  min-height: 0;
  overflow: hidden;
  border-radius: 18px;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
}
.card-face--front {
  align-items: center;
  justify-content: center;
  padding: 8px 2px;
  text-align: center;
}
.card-face--back {
  padding: 8px 2px 4px;
  overflow-y: auto;
  overscroll-behavior: contain;
  -webkit-overflow-scrolling: touch;
  scrollbar-width: thin;
  transform: rotateY(180deg);
}
.card-face--front h2 {
  width: 100%;
  overflow-wrap: anywhere;
  font-size: clamp(2.2rem, 10.5vw, 4rem);
  letter-spacing: -0.055em;
  line-height: 1.04;
  text-align: center;
}
.phonetic, .back-phonetic {
  margin-top: 8px;
  color: #8a8ba8;
  font-family: ui-monospace, monospace;
  text-align: center;
}
.phonetic:empty, .back-phonetic:empty { display: none; }
.flip-hint { margin-top: 16px; color: #9a9bb5; font-size: 0.74rem; letter-spacing: 0.02em; text-align: center; }
.back-content { display: flex; flex-direction: column; align-items: center; width: 100%; margin-block: auto; text-align: center; }
.back-word {
  overflow-wrap: anywhere;
  font-size: clamp(1.7rem, 7vw, 2.1rem);
  letter-spacing: -0.035em;
  line-height: 1.15;
  text-align: center;
}
.meaning-block {
  width: 100%;
  margin-top: 18px;
  padding-top: 16px;
  border-top: 1px solid #f0f0f8;
  text-align: left;
}
.meaning-label {
  margin-bottom: 7px;
  color: var(--brand);
  font-size: 0.68rem;
  font-weight: 800;
  letter-spacing: 0.12em;
}
.meaning {
  padding: 16px;
  border-radius: 14px;
  background: #f7f7fc;
  color: #2f3052;
  font-size: 1.05rem;
  line-height: 1.7;
}
.meaning-list { display: flex; flex-direction: column; gap: 7px; }
.meaning-item { display: flex; align-items: flex-start; gap: 8px; }
.meaning-item::before {
  content: "";
  flex: none;
  width: 5px;
  height: 5px;
  margin-top: 0.62em;
  border-radius: 50%;
  background: var(--brand);
  opacity: 0.45;
}

.card-foot { flex: none; padding-top: 14px; }
.reveal {
  width: 100%;
  padding: 12px;
  border: 0;
  border-radius: 12px;
  background: var(--brand-soft);
  color: #5455c9;
  font-size: 0.88rem;
  font-weight: 750;
  transition: background-color 0.16s ease, transform 0.12s ease;
}
.reveal:hover { background: #e6e7ff; }
.reveal:active { transform: scale(0.99); }

/* Controls stay pinned to the bottom because the card stage grows above them. */
.study-footer { flex: none; margin-top: auto; padding-top: 16px; }
.actions { display: grid; grid-template-columns: repeat(3, 1fr); gap: 10px; }
.actions button, .navigation button, .dialog-actions button, .import-label, .danger {
  border: 0;
  min-height: 52px;
  padding: 10px;
  border-radius: 14px;
  font-weight: 700;
}
.actions button { transition: transform 0.12s ease, filter 0.16s ease; }
.actions button:active { transform: scale(0.985); }
.again { background: var(--again-soft); color: var(--again); }
.hard { background: var(--hard-soft); color: var(--hard); }
.known { background: var(--known-soft); color: var(--known); }
.navigation {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  margin-top: 8px;
}
.navigation button {
  min-height: 44px;
  padding: 8px 10px;
  background: transparent;
  color: #585979;
}
.navigation button:disabled { opacity: 0.4; cursor: default; }
.status { min-height: 1.5em; margin-top: 8px; text-align: center; color: #767797; font-size: 0.8rem; }

dialog {
  width: min(calc(100% - 32px), 460px);
  padding: 0;
  border: 0;
  border-radius: 20px;
  box-shadow: 0 24px 80px rgba(18, 17, 59, 0.28);
}
dialog::backdrop { background: rgba(26, 25, 59, 0.4); }
.dialog-body { padding: 22px; }
.dialog-heading {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}
.dialog-heading button { border: 0; background: transparent; font-size: 1.5rem; }
.dialog-body p { margin: 16px 0; color: #666784; line-height: 1.6; }
.toggle { display: block; margin: 18px 0; }
.dialog-actions { display: grid; grid-template-columns: 1fr 1fr; gap: 10px; }
.dialog-actions button, .import-label {
  display: grid;
  place-items: center;
  background: var(--brand-soft);
  color: #494ac9;
  text-align: center;
}
.danger { width: 100%; margin-top: 16px; color: var(--again); background: var(--again-soft); }

@media (max-width: 599px), (pointer: coarse) {
  .word-card.is-leaving { transition: transform 0.26s ease-out, opacity 0.26s ease-out; }
}
@media (max-width: 420px) {
  .app { padding: 18px 14px max(18px, env(safe-area-inset-bottom)); }
  h1 { font-size: 1.38rem; }
  .progress-region { margin: 20px 0 14px; }
  .deck-picker { margin-bottom: 14px; }
  .deck-box { padding: 9px 12px; border-radius: 14px; }
  .deck-box-icon { width: 32px; height: 32px; border-radius: 10px; }
  .deck-menu { border-radius: 14px; }
  .card-stage { min-height: 280px; }
  .word-card { padding: 15px 16px 14px; border-radius: 22px; }
  .card-face--front h2, .preview-word { font-size: clamp(2rem, 12vw, 3.4rem); }
  .actions { gap: 7px; }
  .actions button { font-size: 0.86rem; }
  .study-footer { padding-top: 12px; }
}
@media (prefers-reduced-motion: reduce) {
  .word-card, .card-inner, .card-preview, .deck-arrow, .progress-thumb, .progress-track i { transition: none !important; }
  .card-preview, .deck-menu { animation: none !important; }
}