:root {
  --bg0: #e8edf5;
  --bg1: #f4f6fa;
  --ink: #1c1c1e;
  --ink-soft: #636366;
  --ink-faint: #8e8e93;
  --card: rgba(255, 255, 255, 0.82);
  --line: rgba(60, 60, 67, 0.12);
  --blue: #0071e3;
  --green: #34c759;
  --amber: #ff9f0a;
  --rose: #ff3b30;
  --shadow: 0 18px 50px rgba(28, 28, 46, 0.12);
  --shadow-soft: 0 8px 28px rgba(28, 28, 46, 0.08);
  --radius: 28px;
  --ease-out: cubic-bezier(0.22, 1, 0.36, 1);
  --ease-spring: cubic-bezier(0.32, 0.72, 0, 1);
  --font: "Outfit", -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  --safe-bottom: env(safe-area-inset-bottom, 0px);
  --safe-top: env(safe-area-inset-top, 0px);
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

html,
body {
  margin: 0;
  min-height: 100%;
}

body {
  font-family: var(--font);
  color: var(--ink);
  background: var(--bg1);
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
  overflow-x: hidden;
}

button {
  font: inherit;
  border: 0;
  background: none;
  color: inherit;
  cursor: pointer;
}

.ambient {
  position: fixed;
  inset: 0;
  z-index: 0;
  background:
    radial-gradient(900px 520px at 12% -10%, rgba(120, 170, 255, 0.35), transparent 60%),
    radial-gradient(700px 480px at 100% 8%, rgba(170, 210, 255, 0.28), transparent 55%),
    radial-gradient(640px 420px at 50% 110%, rgba(200, 190, 255, 0.18), transparent 50%),
    linear-gradient(180deg, var(--bg0), var(--bg1) 48%, #f7f8fb);
  animation: ambientDrift 18s var(--ease-out) infinite alternate;
}

@keyframes ambientDrift {
  from { transform: scale(1) translate3d(0, 0, 0); }
  to { transform: scale(1.04) translate3d(0, -1.5%, 0); }
}

.app {
  position: relative;
  z-index: 1;
  width: min(480px, 100%);
  min-height: 100dvh;
  margin: 0 auto;
  padding:
    calc(16px + var(--safe-top))
    18px
    calc(18px + var(--safe-bottom));
  display: grid;
  grid-template-rows: auto auto 1fr auto;
  gap: 14px;
}

.topbar {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 12px;
  animation: riseIn 0.7s var(--ease-out) both;
}

.brand {
  margin: 0;
  font-size: 1.55rem;
  font-weight: 700;
  letter-spacing: -0.03em;
  line-height: 1.1;
}

.subtitle {
  margin: 4px 0 0;
  font-size: 0.9rem;
  color: var(--ink-soft);
  font-weight: 500;
}

.top-actions {
  display: flex;
  gap: 8px;
  padding-top: 2px;
}

.ghost-btn,
.file-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 34px;
  padding: 0 12px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.55);
  border: 1px solid var(--line);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--ink-soft);
  transition:
    transform 0.28s var(--ease-spring),
    background 0.28s var(--ease-out),
    color 0.28s var(--ease-out);
}

.ghost-btn:active,
.file-btn:active {
  transform: scale(0.94);
  background: rgba(255, 255, 255, 0.9);
  color: var(--ink);
}

.stats {
  display: flex;
  align-items: center;
  gap: 8px;
  flex-wrap: wrap;
  padding: 10px 14px;
  border-radius: 16px;
  background: rgba(255, 255, 255, 0.48);
  border: 1px solid var(--line);
  backdrop-filter: blur(18px);
  -webkit-backdrop-filter: blur(18px);
  font-size: 0.84rem;
  color: var(--ink-soft);
  animation: riseIn 0.75s var(--ease-out) 0.05s both;
}

.stat strong {
  color: var(--ink);
  font-weight: 650;
}

.stat-dot {
  width: 3px;
  height: 3px;
  border-radius: 50%;
  background: var(--ink-faint);
  opacity: 0.7;
}

.stage {
  position: relative;
  display: grid;
  place-items: center;
  min-height: 0;
}

.empty-state {
  width: 100%;
  animation: riseIn 0.55s var(--ease-out) both;
}

.empty-card {
  padding: 36px 24px;
  border-radius: var(--radius);
  background: var(--card);
  border: 1px solid var(--line);
  box-shadow: var(--shadow-soft);
  backdrop-filter: blur(24px);
  -webkit-backdrop-filter: blur(24px);
  text-align: center;
}

.empty-title {
  margin: 0;
  font-size: 1.45rem;
  font-weight: 700;
  letter-spacing: -0.03em;
}

.empty-desc {
  margin: 10px 0 22px;
  color: var(--ink-soft);
  line-height: 1.55;
  font-size: 0.95rem;
}

.primary-btn {
  min-height: 46px;
  padding: 0 22px;
  border-radius: 999px;
  background: var(--ink);
  color: #fff;
  font-weight: 600;
  transition: transform 0.28s var(--ease-spring), opacity 0.28s var(--ease-out);
}

.primary-btn:active {
  transform: scale(0.96);
}

.card-scene {
  width: 100%;
  perspective: 1400px;
}

.card {
  position: relative;
  width: 100%;
  aspect-ratio: 0.78 / 1;
  max-height: min(58dvh, 560px);
  padding: 0;
  border-radius: var(--radius);
  transform-style: preserve-3d;
  transition: transform 0.45s var(--ease-spring);
  animation: cardEnter 0.7s var(--ease-out) both;
}

.card.is-swapping {
  animation: cardSwap 0.55s var(--ease-spring) both;
}

.card:active {
  transform: scale(0.985);
}

.card-inner {
  position: relative;
  width: 100%;
  height: 100%;
  transform-style: preserve-3d;
  transition: transform 0.68s var(--ease-spring);
}

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

.card-face {
  position: absolute;
  inset: 0;
  display: flex;
  flex-direction: column;
  padding: 28px 26px 24px;
  border-radius: var(--radius);
  background:
    linear-gradient(165deg, rgba(255, 255, 255, 0.96), rgba(250, 251, 255, 0.9));
  border: 1px solid rgba(255, 255, 255, 0.7);
  box-shadow: var(--shadow);
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
  overflow: hidden;
}

.card-face::before {
  content: "";
  position: absolute;
  inset: 0 auto auto 0;
  width: 100%;
  height: 120px;
  background: linear-gradient(180deg, rgba(120, 170, 255, 0.12), transparent);
  pointer-events: none;
}

.card-back {
  transform: rotateY(180deg);
}

.face-label {
  position: relative;
  margin: 0;
  font-size: 0.78rem;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--ink-faint);
}

.word {
  position: relative;
  margin: auto 0 12px;
  font-size: clamp(2.4rem, 11vw, 3.4rem);
  font-weight: 700;
  letter-spacing: -0.045em;
  line-height: 1.05;
}

.prompt {
  position: relative;
  margin: 0 0 auto;
  color: var(--ink-soft);
  font-size: 1.05rem;
  line-height: 1.5;
  font-weight: 500;
}

.tap-hint {
  position: relative;
  margin: 18px 0 0;
  color: var(--ink-faint);
  font-size: 0.85rem;
  font-weight: 500;
  opacity: 0.85;
  animation: pulseSoft 2.4s var(--ease-out) infinite;
}

.back-word {
  position: relative;
  margin: 18px 0 8px;
  font-size: 1.8rem;
  font-weight: 700;
  letter-spacing: -0.035em;
}

.core {
  position: relative;
  margin: 0 0 18px;
  font-size: 1.2rem;
  font-weight: 600;
  color: var(--blue);
  letter-spacing: -0.02em;
}

.detail-block {
  position: relative;
  margin-top: auto;
  display: grid;
  gap: 12px;
}

.detail {
  margin: 0;
  color: var(--ink-soft);
  font-size: 0.98rem;
  line-height: 1.5;
  font-weight: 500;
}

.detail.contrast {
  padding: 12px 14px;
  border-radius: 16px;
  background: rgba(120, 170, 255, 0.1);
  color: var(--ink);
}

.example {
  margin: 0;
  font-size: 0.98rem;
  line-height: 1.45;
  font-weight: 550;
  font-style: italic;
  color: var(--ink);
}

.dock {
  display: grid;
  gap: 10px;
  animation: riseIn 0.8s var(--ease-out) 0.08s both;
}

.rate-row {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 10px;
}

.rate-btn {
  display: grid;
  gap: 4px;
  place-items: center;
  min-height: 72px;
  padding: 12px 8px;
  border-radius: 22px;
  background: rgba(255, 255, 255, 0.62);
  border: 1px solid var(--line);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  box-shadow: var(--shadow-soft);
  transition:
    transform 0.32s var(--ease-spring),
    background 0.28s var(--ease-out),
    box-shadow 0.28s var(--ease-out),
    opacity 0.28s var(--ease-out);
}

.rate-btn:disabled {
  opacity: 0.38;
  pointer-events: none;
}

.rate-btn:active {
  transform: scale(0.94);
}

.rate-btn.is-burst {
  animation: rateBurst 0.45s var(--ease-spring);
}

.rate-icon {
  font-size: 1.35rem;
  font-weight: 700;
  line-height: 1;
}

.rate-label {
  font-size: 0.82rem;
  font-weight: 650;
  color: var(--ink-soft);
}

.rate-forgot .rate-icon { color: var(--rose); }
.rate-fuzzy .rate-icon { color: var(--amber); }
.rate-know .rate-icon { color: var(--green); }

.dock-note {
  margin: 0;
  text-align: center;
  font-size: 0.8rem;
  color: var(--ink-faint);
  font-weight: 500;
  min-height: 1.2em;
  transition: opacity 0.3s var(--ease-out);
}

.toast {
  position: fixed;
  left: 50%;
  bottom: calc(28px + var(--safe-bottom));
  z-index: 20;
  transform: translate(-50%, 12px);
  padding: 12px 16px;
  border-radius: 999px;
  background: rgba(28, 28, 30, 0.88);
  color: #fff;
  font-size: 0.88rem;
  font-weight: 600;
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  opacity: 0;
  pointer-events: none;
  transition:
    opacity 0.35s var(--ease-out),
    transform 0.45s var(--ease-spring);
}

.toast.is-on {
  opacity: 1;
  transform: translate(-50%, 0);
}

@keyframes riseIn {
  from {
    opacity: 0;
    transform: translateY(14px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes cardEnter {
  from {
    opacity: 0;
    transform: translateY(28px) scale(0.96);
  }
  to {
    opacity: 1;
    transform: translateY(0) scale(1);
  }
}

@keyframes cardSwap {
  0% {
    opacity: 0;
    transform: translateY(24px) scale(0.96);
  }
  100% {
    opacity: 1;
    transform: translateY(0) scale(1);
  }
}

@keyframes pulseSoft {
  0%, 100% { opacity: 0.55; }
  50% { opacity: 1; }
}

@keyframes rateBurst {
  0% { transform: scale(1); }
  40% { transform: scale(1.06); }
  100% { transform: scale(1); }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}

@media (min-width: 720px) {
  .app {
    padding-top: 28px;
  }

  .card {
    aspect-ratio: 0.82 / 1;
  }
}