:root {
  --bg: #faf6ff;
  --bg-elev: #ffffff;
  --bg-elev-2: #ede3fa;
  --bg-tint: #f3eaff;
  --border: #ddc8ee;
  --border-strong: #b89ee0;
  --text: #2e1f4f;
  --text-dim: #7e6ea8;
  --pink: #e8a5d0;
  --pink-deep: #c97bb8;
  --pink-soft: #f5dff0;
  --mint: #a8e6d3;
  --mint-deep: #5eb7a8;
  --lavender: #c8b6ff;
  --lavender-deep: #9d7cd8;
  --teal: #7dd3c0;
  --teal-deep: #4dac9c;
  --yellow: #ffe7a0;
  --coral: #ffb0b0;
  --coral-deep: #ff8a8a;
  --shadow-soft: 0 6px 20px rgba(157, 124, 216, 0.20);
  --shadow-pop: 0 10px 30px rgba(157, 124, 216, 0.32);
  --radius: 22px;
  --radius-sm: 14px;
  --safe-top: env(safe-area-inset-top, 0px);
  --safe-bottom: env(safe-area-inset-bottom, 0px);
  --rounded-font: ui-rounded, "SF Pro Rounded", "Hiragino Maru Gothic ProN", "Quicksand", "Nunito", "Comfortaa", system-ui, -apple-system, "Segoe UI", sans-serif;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #1a1830;
    --bg-elev: #252040;
    --bg-elev-2: #312955;
    --bg-tint: #1e1b38;
    --border: #4a4070;
    --border-strong: #7560a8;
    --text: #ece2ff;
    --text-dim: #a89cd8;
    --pink: #e8a5d0;
    --pink-deep: #d488c0;
    --pink-soft: #3a2c4f;
    --mint: #9ee0cc;
    --mint-deep: #6ec4ad;
    --lavender: #c8b6ff;
    --lavender-deep: #b89eef;
    --teal: #7dd3c0;
    --teal-deep: #5eb7a8;
    --shadow-soft: 0 6px 20px rgba(0, 0, 0, 0.5);
    --shadow-pop: 0 10px 30px rgba(120, 90, 200, 0.45);
  }
}

* { box-sizing: border-box; }
html, body {
  margin: 0;
  padding: 0;
  background:
    radial-gradient(1200px 600px at 10% -10%, var(--bg-tint), transparent 60%),
    radial-gradient(1000px 500px at 100% 100%, var(--bg-elev-2), transparent 60%),
    var(--bg);
  background-attachment: fixed;
  color: var(--text);
  font-family: var(--rounded-font);
  font-weight: 500;
  -webkit-font-smoothing: antialiased;
  -webkit-tap-highlight-color: transparent;
  overscroll-behavior-y: contain;
}
body {
  min-height: 100dvh;
  display: flex;
  flex-direction: column;
  padding-top: var(--safe-top);
  padding-bottom: var(--safe-bottom);
}

/* Topbar */
#topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
  padding: 10px 14px;
  background: linear-gradient(180deg, var(--bg-tint), var(--bg));
  position: sticky;
  top: var(--safe-top);
  z-index: 5;
  border-bottom: 1px dashed var(--border);
}
#topbar h1 {
  margin: 0;
  font-size: 19px;
  font-weight: 700;
  letter-spacing: 0.3px;
  flex: 1;
  text-align: center;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  background: linear-gradient(135deg, var(--pink-deep), var(--lavender-deep));
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
}
#topbar h1 .butterfly {
  -webkit-text-fill-color: initial;
  display: inline-block;
  font-size: 0.95em;
  animation: flutter 2.4s ease-in-out infinite;
  transform-origin: center;
}
@keyframes flutter {
  0%, 100% { transform: translateY(0) rotate(-6deg) scale(1); }
  25%      { transform: translateY(-3px) rotate(4deg) scale(1.06); }
  50%      { transform: translateY(-1px) rotate(-3deg) scale(0.98); }
  75%      { transform: translateY(-4px) rotate(6deg) scale(1.04); }
}

.icon-btn, .text-btn {
  background: transparent;
  border: none;
  color: var(--text);
  cursor: pointer;
  padding: 8px;
  border-radius: 14px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font: inherit;
  transition: transform .15s, background .15s;
}
.text-btn {
  padding: 8px 14px;
  font-size: 14px;
  font-weight: 700;
  color: #fff;
  background: linear-gradient(135deg, var(--pink), var(--pink-deep));
  border-radius: 999px;
  box-shadow: var(--shadow-soft);
}
.text-btn:active { transform: scale(0.95); }
.icon-btn:active { background: var(--bg-elev-2); transform: scale(0.92); }
.icon-btn[hidden], .text-btn[hidden] { display: none; }

main#view {
  flex: 1;
  width: 100%;
  max-width: 760px;
  margin: 0 auto;
  padding: 20px 18px 32px;
  display: flex;
  flex-direction: column;
  position: relative;
}

/* Decorative butterflies + sparkles in corners */
main#view::before, main#view::after {
  position: absolute;
  pointer-events: none;
  animation: float 4s ease-in-out infinite;
}
main#view::before {
  content: "🦋";
  font-size: 20px;
  opacity: 0.7;
  top: 8px; right: 18px;
}
main#view::after {
  content: "✨";
  font-size: 14px;
  opacity: 0.55;
  top: 60px; left: 12px;
  animation-delay: -2s;
}
@keyframes float {
  0%, 100% { transform: translateY(0) rotate(-4deg); }
  50%      { transform: translateY(-7px) rotate(10deg); }
}

/* Home */
.home-actions {
  display: flex;
  flex-direction: column;
  gap: 12px;
  margin-bottom: 18px;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 16px 18px;
  border-radius: 999px;
  border: 2px solid var(--border-strong);
  background: var(--bg-elev);
  color: var(--text);
  font-family: var(--rounded-font);
  font-size: 15px;
  font-weight: 700;
  cursor: pointer;
  text-align: center;
  box-shadow: var(--shadow-soft);
  transition: transform .15s, box-shadow .15s, background .15s;
}
.btn:active { transform: translateY(1px) scale(0.98); box-shadow: 0 2px 8px rgba(255,143,184,0.2); }
.btn.primary {
  background: linear-gradient(135deg, var(--pink), var(--pink-deep));
  border-color: var(--pink-deep);
  color: #fff;
  box-shadow: var(--shadow-pop);
}
.btn.primary:active { background: linear-gradient(135deg, var(--pink-deep), var(--pink)); }
.btn.ghost { background: transparent; border-color: var(--border); box-shadow: none; }
.btn.danger { color: var(--coral-deep); border-color: var(--coral); }
.btn[disabled] { opacity: 0.5; pointer-events: none; }

.deck-list {
  display: flex;
  flex-direction: column;
  gap: 12px;
}
.deck-card {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  background: var(--bg-elev);
  border: 2px solid var(--border);
  border-radius: var(--radius);
  padding: 16px 18px;
  cursor: pointer;
  text-align: left;
  width: 100%;
  font: inherit;
  color: var(--text);
  box-shadow: var(--shadow-soft);
  transition: transform .15s, border-color .15s, box-shadow .15s;
  position: relative;
  overflow: hidden;
}
.deck-card::before {
  content: "";
  position: absolute;
  top: -20px; right: -20px;
  width: 60px; height: 60px;
  background: radial-gradient(circle, var(--pink-soft), transparent 70%);
  pointer-events: none;
}
.deck-card:active { transform: translateY(1px) scale(0.99); border-color: var(--pink); }
.deck-card .meta { flex: 1; min-width: 0; }
.deck-card .name {
  font-weight: 700;
  font-size: 17px;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}
.deck-card .sub {
  font-size: 13px;
  color: var(--text-dim);
  margin-top: 4px;
  font-weight: 600;
}
.deck-card .chev { color: var(--pink); flex-shrink: 0; }

.empty {
  text-align: center;
  color: var(--text-dim);
  padding: 24px 16px 28px;
  border: 2px dashed var(--border-strong);
  border-radius: var(--radius);
  margin-top: 8px;
  background: var(--bg-elev);
}
.empty .mascot {
  width: 110px;
  height: 110px;
  margin: 0 auto 8px;
  animation: bobble 3s ease-in-out infinite;
}
@keyframes bobble {
  0%, 100% { transform: translateY(0) rotate(-2deg); }
  50% { transform: translateY(-6px) rotate(2deg); }
}
.empty h3 { margin: 0 0 6px; color: var(--text); font-size: 18px; font-weight: 700; }
.empty p { margin: 0; font-size: 14px; line-height: 1.5; font-weight: 500; }
.empty code {
  background: var(--pink-soft);
  color: var(--pink-deep);
  padding: 2px 8px;
  border-radius: 8px;
  font-size: 13px;
  font-weight: 700;
  font-family: var(--rounded-font);
}

.drop-zone {
  border: 2px dashed var(--border-strong);
  border-radius: var(--radius);
  padding: 18px;
  text-align: center;
  color: var(--text-dim);
  margin-top: 14px;
  background: var(--bg-elev);
  font-weight: 600;
  font-size: 14px;
  transition: border-color .15s, background .15s, transform .15s;
}
.drop-zone.dragover {
  border-color: var(--pink);
  background: var(--pink-soft);
  color: var(--pink-deep);
  transform: scale(1.02);
}

/* Deck detail */
.deck-header { margin-bottom: 14px; }
.deck-header h2 {
  margin: 0 0 4px;
  font-size: 24px;
  font-weight: 800;
  color: var(--text);
}
.deck-header .stats {
  color: var(--text-dim);
  font-size: 14px;
  font-weight: 600;
}

.tag-row {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin: 14px 0 6px;
}
.tag {
  background: var(--bg-elev);
  border: 1.5px solid var(--border);
  color: var(--text);
  padding: 6px 12px;
  border-radius: 999px;
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0.01em;
  cursor: pointer;
  user-select: none;
  transition: transform .12s, background .12s;
}
.tag:active { transform: scale(0.94); }
.tag.active {
  background: linear-gradient(135deg, var(--pink), var(--pink-deep));
  color: #fff;
  border-color: var(--pink-deep);
}
.tag.pastel-0 { background: #ffe0ee; border-color: #ff9fc4; color: #7a1f48; }
.tag.pastel-1 { background: #e2f4ec; border-color: #7fcaa8; color: #1f5a44; }
.tag.pastel-2 { background: #e8e0ff; border-color: #a890f0; color: #3d2a78; }
.tag.pastel-3 { background: #fff5d4; border-color: #e8c560; color: #6b4e10; }
.tag.pastel-4 { background: #d6efff; border-color: #7fbde8; color: #1d4870; }
.tag.pastel-0.active, .tag.pastel-1.active, .tag.pastel-2.active,
.tag.pastel-3.active, .tag.pastel-4.active {
  background: linear-gradient(135deg, var(--pink), var(--pink-deep));
  border-color: var(--pink-deep);
  color: #fff;
}

.action-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 10px;
  margin: 14px 0;
}

.cards-list { margin-top: 8px; }
.card-row {
  display: flex;
  flex-direction: column;
  gap: 4px;
  padding: 14px 16px;
  background: var(--bg-elev);
  border: 1.5px solid var(--border);
  border-radius: var(--radius-sm);
  margin-bottom: 8px;
  box-shadow: var(--shadow-soft);
}
.card-row .front { font-weight: 700; font-size: 15px; }
.card-row .back { color: var(--text-dim); font-size: 14px; font-weight: 500; }
.card-row .row-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 4px;
  margin-top: 6px;
}
.card-row .row-tags .tag {
  font-size: 12px;
  padding: 3px 9px;
  font-weight: 700;
  cursor: default;
}

/* Study */
.study {
  display: flex;
  flex-direction: column;
  flex: 1;
  gap: 14px;
}
.progress {
  display: flex;
  justify-content: space-between;
  font-size: 13px;
  color: var(--text-dim);
  font-weight: 700;
}
.progress-bar {
  height: 10px;
  background: var(--bg-elev-2);
  border-radius: 999px;
  overflow: hidden;
  border: 1.5px solid var(--border);
  position: relative;
}
.progress-bar > span {
  display: block;
  height: 100%;
  background: linear-gradient(90deg, var(--pink), var(--lavender), var(--pink-deep));
  background-size: 200% 100%;
  border-radius: 999px;
  transition: width .35s cubic-bezier(.2,.8,.2,1);
  animation: shimmer 3s linear infinite;
}
@keyframes shimmer {
  0% { background-position: 0% 0; }
  100% { background-position: 200% 0; }
}

.flashcard-wrap {
  flex: 1;
  display: flex;
  align-items: center;
  justify-content: center;
  perspective: 1400px;
  min-height: 260px;
  touch-action: pan-y;
  position: relative;
}
.flashcard {
  width: 100%;
  max-width: 560px;
  aspect-ratio: 3 / 2;
  position: relative;
  transform-style: preserve-3d;
  transition: transform .45s cubic-bezier(.2,.8,.2,1);
  cursor: pointer;
  user-select: none;
  -webkit-user-select: none;
}
.flashcard.flipped { transform: rotateY(180deg); }
.flashcard.wiggle { animation: wiggle 0.5s ease; }
.flashcard.zoom-out { animation: zoom-out 0.35s ease forwards; }
@keyframes wiggle {
  0%, 100% { transform: translateX(0) rotate(0); }
  20% { transform: translateX(-8px) rotate(-2deg); }
  40% { transform: translateX(8px) rotate(2deg); }
  60% { transform: translateX(-6px) rotate(-1.5deg); }
  80% { transform: translateX(6px) rotate(1.5deg); }
}
@keyframes zoom-out {
  to { transform: scale(0.6) translateY(-40px); opacity: 0; }
}

.flashcard .face {
  position: absolute;
  inset: 0;
  background: var(--bg-elev);
  border: 3px solid var(--border-strong);
  border-radius: 28px;
  box-shadow: var(--shadow-pop);
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 28px;
  text-align: center;
  font-size: clamp(20px, 4.4vw, 30px);
  font-weight: 600;
  line-height: 1.3;
  -webkit-backface-visibility: hidden;
  backface-visibility: hidden;
  word-break: break-word;
  overflow: auto;
  background-image: radial-gradient(circle at 12% 12%, var(--pink-soft), transparent 30%),
                    radial-gradient(circle at 88% 88%, #e8e0ff, transparent 30%);
}
.flashcard .face.back {
  transform: rotateY(180deg);
  background-image: radial-gradient(circle at 88% 12%, #e2f4ec, transparent 30%),
                    radial-gradient(circle at 12% 88%, var(--pink-soft), transparent 30%);
}
.flashcard .face .label {
  position: absolute;
  top: 12px;
  left: 16px;
  font-size: 11px;
  letter-spacing: 0.12em;
  color: var(--pink-deep);
  text-transform: uppercase;
  font-weight: 800;
  background: var(--pink-soft);
  padding: 3px 10px;
  border-radius: 999px;
}
.flashcard .face .corner {
  position: absolute;
  font-size: 18px;
  opacity: 0.55;
}
.flashcard .face .corner.tr { top: 12px; right: 14px; }
.flashcard .face .corner.bl { bottom: 12px; left: 14px; }
.flashcard .face .card-tags {
  position: absolute;
  bottom: 12px;
  left: 0;
  right: 0;
  display: flex;
  flex-wrap: wrap;
  gap: 4px;
  justify-content: center;
  padding: 0 14px;
}
.flashcard .face .card-tags .tag {
  font-size: 11px;
  padding: 3px 9px;
  font-weight: 700;
  cursor: default;
}

.study-controls {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
}
.study-controls .btn { padding: 18px 12px; font-size: 16px; }
.btn.again {
  color: #fff;
  background: linear-gradient(135deg, var(--coral), var(--coral-deep));
  border-color: var(--coral-deep);
  box-shadow: 0 6px 20px rgba(255, 138, 138, 0.35);
}
.btn.good {
  color: #fff;
  background: linear-gradient(135deg, var(--mint), var(--mint-deep));
  border-color: var(--mint-deep);
  box-shadow: 0 6px 20px rgba(79, 207, 166, 0.35);
}
.study-hint {
  text-align: center;
  font-size: 13px;
  color: var(--text-dim);
  font-weight: 600;
}

/* Particles */
.particle {
  position: fixed;
  font-size: 22px;
  pointer-events: none;
  z-index: 200;
  animation: particle-fly 0.9s ease-out forwards;
  transform: translate(-50%, -50%);
  will-change: transform, opacity;
}
@keyframes particle-fly {
  0%   { transform: translate(-50%, -50%) scale(0) rotate(0); opacity: 0; }
  20%  { transform: translate(-50%, -50%) scale(1.2) rotate(20deg); opacity: 1; }
  100% { transform: translate(calc(-50% + var(--dx)), calc(-50% + var(--dy))) scale(0.4) rotate(360deg); opacity: 0; }
}

/* Confetti */
.confetti {
  position: fixed;
  top: -40px;
  pointer-events: none;
  z-index: 200;
  animation-name: confetti-fall;
  animation-timing-function: ease-in;
  animation-fill-mode: forwards;
  will-change: transform;
}
@keyframes confetti-fall {
  0%   { transform: translateY(0) rotate(0); opacity: 1; }
  100% { transform: translateY(110vh) rotate(720deg); opacity: 0.85; }
}

/* Toast */
#toast {
  position: fixed;
  left: 50%;
  bottom: calc(20px + var(--safe-bottom));
  transform: translateX(-50%) translateY(20px);
  background: var(--bg-elev);
  color: var(--text);
  border: 2px solid var(--border-strong);
  padding: 12px 18px;
  border-radius: 999px;
  font-size: 14px;
  font-weight: 700;
  box-shadow: var(--shadow-pop);
  opacity: 0;
  pointer-events: none;
  transition: opacity .2s, transform .2s;
  max-width: calc(100vw - 32px);
  text-align: center;
  z-index: 100;
}
#toast.show {
  opacity: 1;
  transform: translateX(-50%) translateY(0);
}

/* Modal */
.modal-backdrop {
  position: fixed;
  inset: 0;
  background: rgba(70, 30, 50, 0.4);
  backdrop-filter: blur(4px);
  -webkit-backdrop-filter: blur(4px);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 50;
  padding: 16px;
  animation: fade-in 0.2s ease;
}
@keyframes fade-in { from { opacity: 0; } to { opacity: 1; } }
.modal {
  background: var(--bg-elev);
  border: 3px solid var(--border-strong);
  border-radius: var(--radius);
  padding: 22px;
  max-width: 420px;
  width: 100%;
  box-shadow: var(--shadow-pop);
  animation: pop-in 0.3s cubic-bezier(.2,1.6,.4,1);
}
@keyframes pop-in {
  from { transform: scale(0.85); opacity: 0; }
  to { transform: scale(1); opacity: 1; }
}
.modal h3 { margin: 0 0 8px; font-size: 18px; font-weight: 800; color: var(--pink-deep); }
.modal p { margin: 0 0 14px; color: var(--text-dim); font-size: 14px; line-height: 1.4; font-weight: 600; }
.modal input[type="text"] {
  width: 100%;
  padding: 14px 16px;
  border-radius: 14px;
  border: 2px solid var(--border);
  background: var(--bg);
  color: var(--text);
  font-family: var(--rounded-font);
  font-weight: 600;
  font-size: 15px;
  margin-bottom: 14px;
}
.modal input[type="text"]:focus {
  outline: none;
  border-color: var(--pink);
  box-shadow: 0 0 0 4px var(--pink-soft);
}
.modal-actions {
  display: flex;
  gap: 8px;
  justify-content: flex-end;
}

/* Done screen */
.done-screen {
  flex: 1;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
  gap: 16px;
  padding: 24px 8px;
}
.done-screen .mascot {
  width: 140px;
  height: 140px;
  animation: cheer 1.4s ease-in-out infinite;
}
@keyframes cheer {
  0%, 100% { transform: translateY(0) rotate(-4deg); }
  50% { transform: translateY(-10px) rotate(4deg); }
}
.done-screen h2 {
  margin: 0;
  font-size: 30px;
  font-weight: 800;
  background: linear-gradient(135deg, var(--pink-deep), var(--lavender-deep));
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}
.done-screen p { margin: 0; color: var(--text-dim); font-weight: 600; }
.done-screen .stats-row {
  display: flex;
  gap: 14px;
  margin: 8px 0;
}
.done-screen .stat {
  background: var(--bg-elev);
  border: 2px solid var(--border-strong);
  border-radius: var(--radius);
  padding: 14px 22px;
  box-shadow: var(--shadow-soft);
  min-width: 96px;
}
.done-screen .stat .num { font-size: 30px; font-weight: 800; color: var(--pink-deep); }
.done-screen .stat .lbl {
  font-size: 11px;
  color: var(--text-dim);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  font-weight: 700;
}
.done-screen .actions {
  display: flex;
  flex-direction: column;
  gap: 10px;
  width: 100%;
  max-width: 320px;
  margin-top: 6px;
}

@media (min-width: 600px) {
  main#view { padding: 28px 24px 40px; }
  .action-grid { grid-template-columns: repeat(3, 1fr); }
}