:root{
  --bg:#1c0e18;
  --bg-deep:#120810;
  --surface:#2a1424;
  --surface-2:#331a30;
  --surface-3:#3d1f38;
  --card:#2e1428;
  --card-front:#38182f;
  --line:#6b2c53;
  --line-bright:#a83d7c;
  --ink:#fff3f8;
  --muted:#dba8c4;
  --pink:#ff4f9e;
  --pink-soft:#ffa8d4;
  --green:#18e58a;
  --red:#ff5365;
  --shadow:0 18px 55px rgba(0,0,0,.42);
}

*{box-sizing:border-box}
html{background:var(--bg-deep)}
body{
  margin:0;
  min-height:100vh;
  background:
    radial-gradient(circle at 50% 12%,rgba(178,40,110,.18),transparent 34%),
    linear-gradient(180deg,var(--bg) 0%,var(--bg-deep) 100%);
  color:var(--ink);
  font-family:system-ui,-apple-system,BlinkMacSystemFont,"Segoe UI",sans-serif;
  -webkit-font-smoothing:antialiased;
}

button,input,textarea,select{font:inherit}
button{color:inherit}

.app{
  width:min(920px,100%);
  min-height:100vh;
  margin:auto;
  padding:18px 18px 105px;
}

/* ---------------------------------------------------------------
   HEADER
   --------------------------------------------------------------- */
.top{text-align:left;padding:4px 4px 13px}
.top h1{margin:0;font-size:clamp(1.45rem,4vw,2rem);font-weight:800;letter-spacing:-.03em}
.top h1::first-letter{color:var(--pink)}
.top p{margin:3px 0 0;color:var(--pink-soft);font-size:.88rem;font-weight:600}

/* Main subject selector: deliberately horizontal on phones. */
.subjects{
  display:flex;
  gap:10px;
  overflow-x:auto;
  padding:2px 2px 14px;
  scrollbar-width:none;
  -webkit-overflow-scrolling:touch;
}
.subjects::-webkit-scrollbar{display:none}
.subject{
  flex:0 0 auto;
  border:1px solid var(--line);
  background:linear-gradient(180deg,#3a1a34,#210f1e);
  color:#e9c8dc;
  border-radius:999px;
  padding:10px 16px;
  white-space:nowrap;
  font-weight:700;
  cursor:pointer;
  box-shadow:inset 0 1px rgba(255,255,255,.04);
  transition:.18s ease;
}
.subject.active{
  color:#fff;
  border-color:var(--pink);
  background:linear-gradient(180deg,#e0227f,#a91760);
  box-shadow:0 0 18px rgba(224,34,127,.28),inset 0 1px rgba(255,255,255,.18);
}

.streak-badge{
  display:flex;
  justify-content:center;
  gap:7px;
  color:var(--muted);
  font-size:.78rem;
  margin:-2px 0 9px;
}

/* Topic selector becomes a compact horizontal strip. */
.chips{
  display:flex;
  flex-wrap:nowrap;
  gap:8px;
  overflow-x:auto;
  padding:3px 2px 13px;
  scrollbar-width:none;
  -webkit-overflow-scrolling:touch;
}
.chips::-webkit-scrollbar{display:none}
.chip{
  flex:0 0 auto;
  border:1px solid var(--line);
  background:#241220;
  color:#d9a8c4;
  border-radius:999px;
  padding:8px 13px;
  cursor:pointer;
  font-size:.8rem;
}
.chip.active{
  color:#fff;
  background:#3d1836;
  border-color:#b93d80;
  box-shadow:inset 0 0 0 1px rgba(224,34,127,.12);
}

.formula-tools{display:flex;flex-wrap:wrap;gap:8px;margin-bottom:12px}
.formula-search-row{display:flex;gap:8px;width:100%}
.formula-search-row input{
  flex:1;
  min-width:0;
  border:1px solid var(--line);
  border-radius:12px;
  padding:11px 13px;
  color:var(--ink);
  background:#200f1c;
  outline:none;
}
.formula-search-row input:focus{border-color:var(--pink);box-shadow:0 0 0 3px rgba(224,34,127,.1)}
.formula-search-row button,.next-btn{
  border:1px solid var(--pink);
  border-radius:12px;
  padding:10px 14px;
  background:linear-gradient(180deg,#d81e78,#a3155e);
  color:#fff;
  font-weight:750;
  cursor:pointer;
}
#formulaSearchInfo{font-size:.76rem;color:var(--muted);min-height:17px}

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

/* ---------------------------------------------------------------
   FLASHCARD
   --------------------------------------------------------------- */
.deck-meta{
  display:flex;
  justify-content:space-between;
  align-items:center;
  color:var(--muted);
  font-size:.78rem;
  margin:4px 5px 10px;
}
.deck-meta strong{color:var(--ink)}

.card-stage{perspective:1400px;padding:0 4px}
.flashcard{
  position:relative;
  min-height:480px;
  transform-style:preserve-3d;
  transition:transform .5s cubic-bezier(.2,.7,.2,1);
  cursor:pointer;
}
/* Flashcard depth is provided by the card shadow.
   No pseudo-element layers are used here because they
   interfere with the 3D back-face rendering. */
.flashcard.flipped{transform:rotateY(180deg)}

.face{
  position:absolute;
  inset:0;
  backface-visibility:hidden;
  -webkit-backface-visibility:hidden;
  background:
    radial-gradient(circle at 80% 5%,rgba(224,34,127,.12),transparent 32%),
    linear-gradient(145deg,#3a1a34 0%,#26122a 52%,#170b1c 100%);
  border:1px solid #8a3468;
  border-radius:27px;
  padding:32px 28px;
  display:flex;
  flex-direction:column;
  align-items:center;
  justify-content:center;
  text-align:center;
  box-shadow:var(--shadow),inset 0 1px rgba(255,255,255,.07);
  overflow:hidden;
}
.face::before{
  content:"";
  position:absolute;
  inset:0;
  border-radius:inherit;
  pointer-events:none;
  box-shadow:inset 0 0 45px rgba(0,0,0,.2);
}
.back{transform:rotateY(180deg)}

.topic-tag{
  align-self:flex-start;
  font-size:.76rem;
  color:#ffe6f3;
  font-weight:800;
  background:#a3155e;
  border:1px solid #d63c8c;
  border-radius:9px;
  padding:7px 11px;
}
.face h2{
  width:100%;
  font-size:clamp(1.65rem,5vw,2.25rem);
  line-height:1.12;
  margin:22px 0 10px;
  letter-spacing:-.025em;
}
.hint,.desc{color:#d9b8cc;line-height:1.6}
.hint{font-size:.9rem}
.formula{
  width:100%;
  margin:25px 0 22px;
  padding:22px 14px;
  border:2px solid #e0227f;
  border-radius:20px;
  background:linear-gradient(145deg,#7a1a56,#4f1140);
  box-shadow:0 0 24px rgba(224,34,127,.15),inset 0 1px rgba(255,255,255,.06);
  font-size:clamp(1.65rem,6vw,2.6rem);
  line-height:1.25;
  font-weight:800;
  color:#fff;
  overflow-x:auto;
}
.tip-line{
  width:100%;
  margin:4px 0 0;
  padding:14px 16px;
  border:1px solid #7a2e5c;
  border-radius:16px;
  color:#ffd6ec;
  background:rgba(58,20,48,.65);
  font-size:.88rem;
  line-height:1.55;
}
.mastered-mark{position:absolute;right:24px;top:20px;color:var(--green);font-size:1.4rem;font-weight:800}
.edit-card-btn{
  position:relative;
  z-index:2;
  margin-top:18px;
  border:1px solid #a83d78;
  border-radius:11px;
  padding:9px 15px;
  background:rgba(50,18,42,.82);
  color:#ffd6ec;
  font-size:.82rem;
  font-weight:750;
  cursor:pointer;
  box-shadow:inset 0 1px rgba(255,255,255,.05);
}
.edit-card-btn:hover,.edit-card-btn:focus-visible{
  border-color:var(--pink);
  color:#fff;
  outline:none;
}
.modal-subtitle{color:var(--muted);font-size:.84rem;line-height:1.45;margin:-4px 0 12px}


.deck-controls{
  display:flex;
  align-items:center;
  justify-content:space-between;
  gap:10px;
  margin:20px 4px 0;
}
.icon-btn{
  flex:0 0 58px;
  height:54px;
  border:1px solid #7a2e5c;
  background:#2e1428;
  color:#ffe0ef;
  border-radius:999px;
  font-size:2rem;
  line-height:1;
  cursor:pointer;
  box-shadow:0 8px 22px rgba(0,0,0,.22),inset 0 1px rgba(255,255,255,.05);
}
.mark-row{display:flex;flex:1;gap:10px;max-width:560px}
.mark-btn{
  flex:1;
  min-height:54px;
  border:2px solid;
  border-radius:999px;
  padding:10px 14px;
  cursor:pointer;
  font-weight:800;
  font-size:.98rem;
  background:transparent;
}
.mark-btn.no{color:#ff6877;border-color:#ff5365;background:rgba(104,10,28,.34);box-shadow:0 0 18px rgba(255,83,101,.1)}
.mark-btn.yes{color:#20ee96;border-color:#18e58a;background:rgba(3,91,56,.35);box-shadow:0 0 18px rgba(24,229,138,.1)}

/* Add-card tile: last card of every deck, lets the user add a new fiche. */
body.add-card-active .flashcard{border:2px dashed var(--pink);box-shadow:none}
body.add-card-active .face{background:rgba(56,24,47,.55)}
body.add-card-active #frontName{color:var(--pink-soft)}
body.add-card-active .edit-card-btn,body.add-card-active .expand-card-btn{display:none}
body.add-card-active .mark-row{visibility:hidden;pointer-events:none}


/* ---------------------------------------------------------------
   PAIRS GAME
   --------------------------------------------------------------- */
.pairs-head{display:flex;align-items:center;justify-content:space-between;gap:12px;margin:4px 0 12px}
.pairs-head h2{margin:0;font-size:1.35rem}
.pairs-head p{margin:4px 0 0;color:var(--muted);font-size:.8rem}
.pairs-stats{display:flex;justify-content:space-between;color:var(--muted);font-size:.8rem;margin:0 3px 10px}
.pairs-grid{display:grid;grid-template-columns:repeat(5,minmax(0,1fr));gap:10px;overflow:visible}
.pair-tile{position:relative;z-index:1;min-width:0;aspect-ratio:1/1.18;border:0;padding:0;background:none;perspective:900px;cursor:pointer;transition:transform .2s ease,filter .2s ease}
.pair-tile:disabled{cursor:default}
.pair-card-inner{position:absolute;inset:0;display:block;transform-style:preserve-3d;transition:transform .38s cubic-bezier(.2,.7,.2,1)}
.pair-tile.is-open{z-index:10;transform:scale(1.10)}
.pair-tile.is-open .pair-card-inner{transform:rotateY(180deg)}
.pair-face{position:absolute;inset:0;display:flex;flex-direction:column;align-items:center;justify-content:center;padding:9px;border-radius:14px;backface-visibility:hidden;-webkit-backface-visibility:hidden;text-align:center;overflow:hidden}
.pair-cover{background:linear-gradient(145deg,#3a1a3a,#25102a);border:1px solid #8a3468;color:#ff7ab8;font-size:2rem;font-weight:850;box-shadow:0 8px 20px rgba(0,0,0,.24),inset 0 1px rgba(255,255,255,.06)}
.pair-cover::after{content:"";position:absolute;inset:6px;border:1px solid rgba(255,122,184,.15);border-radius:10px}
.pair-content{transform:rotateY(180deg);background:linear-gradient(145deg,#3d1a3d,#280f2a);border:2px solid #e0227f;color:var(--ink);gap:8px;box-shadow:0 18px 38px rgba(0,0,0,.48),0 0 24px rgba(224,34,127,.22),inset 0 1px rgba(255,255,255,.08)}
.pair-tile.is-open .pair-cover{box-shadow:0 18px 38px rgba(0,0,0,.48),0 0 24px rgba(224,34,127,.22),inset 0 1px rgba(255,255,255,.08)}
.pair-topic{font-size:.58rem;color:var(--pink-soft);font-weight:700;line-height:1.2}
.pair-content strong{font-size:.82rem;line-height:1.22}
.pair-formula{font-size:.82rem;line-height:1.25;font-weight:850;word-break:break-word}
.pair-tile.is-matched{opacity:.28}
.pair-tile.is-matched .pair-card-inner{transform:rotateY(180deg)}
.pair-tile:focus-visible{outline:2px solid var(--pink);outline-offset:2px;border-radius:15px}
.pairs-help{margin:14px 2px 0;color:var(--muted);font-size:.78rem;line-height:1.45;text-align:center}
.pairs-win{margin:14px 0;padding:12px;border:1px solid #1b9364;border-radius:12px;background:rgba(3,91,56,.25);text-align:center;color:#b9ffdf;font-weight:750}

/* ---------------------------------------------------------------
   OTHER VIEWS
   --------------------------------------------------------------- */
.panel{
  background:linear-gradient(145deg,#341a30,#210f1e);
  border:1px solid var(--line);
  border-radius:20px;
  padding:20px;
  box-shadow:var(--shadow);
}
.panel h2{margin-top:0}
.answer{
  display:block;
  width:100%;
  text-align:left;
  margin:9px 0;
  padding:13px;
  border:1px solid var(--line);
  border-radius:12px;
  background:#241220;
  color:var(--ink);
  cursor:pointer;
}
.answer:disabled{cursor:default}
.correct{border-color:#269a69;background:#083b29}
.wrong{border-color:#b94d5b;background:#421822}
.calc-row{display:grid;grid-template-columns:1fr 1fr;gap:8px}
.calc-row input{width:100%;padding:11px;border:1px solid var(--line);border-radius:10px;background:#200f1c;color:#fff}
.statbar{height:9px;background:#351830;border-radius:99px;overflow:hidden}
.statbar i{display:block;height:100%;background:linear-gradient(90deg,#d81e78,#ff7ab8)}
.stat{margin:14px 0}

/* Bottom navigation remains thumb-friendly and visually quiet. */
.tabs{
  position:fixed;
  z-index:20;
  bottom:0;
  left:50%;
  transform:translateX(-50%);
  width:min(920px,100%);
  display:grid;
  grid-template-columns:repeat(5,1fr);
  background:rgba(20,9,16,.96);
  border-top:1px solid #4a2040;
  padding:8px 10px calc(8px + env(safe-area-inset-bottom));
  backdrop-filter:blur(16px);
  -webkit-backdrop-filter:blur(16px);
}
.tab{
  position:relative;
  border:0;
  background:none;
  padding:7px 2px 8px;
  color:#c98cae;
  cursor:pointer;
  font-weight:650;
}
.tab.active{color:#ff5fa8}
.tab.active::after{
  content:"";
  position:absolute;
  left:15%;right:15%;bottom:0;
  height:3px;
  border-radius:3px;
  background:var(--pink);
  box-shadow:0 0 10px rgba(224,34,127,.7);
}
.tab span{display:block;font-size:1.25rem;line-height:1;margin-bottom:4px}

.modal{position:fixed;inset:0;background:rgba(15,6,12,.82);display:grid;place-items:center;padding:16px;z-index:30}
.modal>div{width:min(520px,100%);background:#2c1428;border:1px solid #7a2e5c;color:var(--ink);border-radius:20px;padding:20px;box-shadow:var(--shadow)}
.modal label{display:block;font-size:.82rem;font-weight:700;margin:11px 0}
.modal input,.modal select,.modal textarea{display:block;width:100%;margin-top:5px;padding:10px;border:1px solid var(--line);border-radius:9px;background:#200f1c;color:#fff;font:inherit}
.actions{display:flex;justify-content:flex-end;gap:8px;margin-top:14px}
.actions button{padding:9px 12px;border-radius:9px;border:1px solid var(--line);background:#2c1428;cursor:pointer}
.actions .primary{background:#d81e78;color:#fff;border-color:#e0227f}
.actions .danger{background:#4a0e16;color:#ff8b93;border-color:#c23545;margin-right:auto}

/* Desktop: use the same visual language but give the card more room. */
@media(min-width:760px){
  .app{padding-top:28px}
  .top{text-align:center}
  .flashcard{min-height:560px}
  .face{padding:42px 46px}
}

/* Phone-first tuning. */
@media(max-width:600px){
  .app{padding:12px 10px 102px}
  .top{padding:4px 3px 9px}
  .top h1{font-size:1.5rem}
  .subjects{gap:8px;padding-bottom:10px}
  .subject{padding:9px 13px;font-size:.88rem}
  .streak-badge{display:none}
  .chips{padding-bottom:11px}
  .formula-tools{display:none}
  .pairs-head{align-items:flex-start}
  .pairs-head h2{font-size:1.15rem}
  .pairs-head .next-btn{padding:8px 10px;font-size:.76rem}
  .pairs-grid{gap:7px}
  .pair-face{padding:6px;border-radius:11px}
  .pair-cover{font-size:1.55rem}
  .pair-topic{font-size:.5rem}
  .pair-content strong,.pair-formula{font-size:.67rem}
  .pair-tile.is-open{transform:scale(1.09)}
  .deck-meta{margin-top:3px}
  .card-stage{padding:0 1px}
  .flashcard{min-height:470px}
  .face{padding:25px 18px;border-radius:25px}
  .face h2{font-size:1.72rem}
  .formula{font-size:1.55rem;padding:20px 10px;margin:19px 0 18px}
  .desc{font-size:.91rem}
  .tip-line{font-size:.82rem}
  .deck-controls{margin-top:18px}
  .icon-btn{flex-basis:52px;height:52px}
  .mark-btn{min-height:52px;padding:9px 7px;font-size:.9rem}
}

@media(max-width:360px){
  .flashcard{min-height:440px}
  .face{padding:22px 14px}
  .mark-row{gap:6px}
  .mark-btn{font-size:.82rem}
  .icon-btn{flex-basis:46px}
}
/* ============================================================
   FLASHCARD CONTENT VISIBILITY FIX
   ============================================================ */

.flashcard .face{
  position:absolute;
  isolation:isolate;
}

.flashcard .face::before{
  z-index:0;
}

.flashcard .face > *{
  position:relative;
  z-index:2;
}

.flashcard .back{
  transform:rotateY(180deg);
  backface-visibility:hidden;
  -webkit-backface-visibility:hidden;
}
/* Larger, more readable text in Paires */
.pair-topic{
  font-size:.72rem;
}

.pair-content strong{
  font-size:1rem;
  line-height:1.25;
}

.pair-formula{
  font-size:1rem;
  line-height:1.3;
}
/* ============================================================ */

/* Easier left-to-right matching game */
.match-head{display:flex;align-items:center;justify-content:space-between;gap:12px;margin:4px 0 10px}.match-head h2{margin:0;font-size:1.35rem}.match-head p{margin:4px 0 0;color:var(--muted);font-size:.8rem}.match-stats{display:flex;justify-content:space-between;color:var(--muted);font-size:.8rem;margin:0 3px 8px}.match-help{text-align:center;color:var(--muted);font-size:.8rem;margin:0 0 12px}.match-grid{display:grid;grid-template-columns:minmax(0,1fr) minmax(0,1fr);gap:12px;align-items:start}.match-column{display:flex;flex-direction:column;gap:8px;min-width:0}.match-column-title{text-align:center;color:var(--muted);font-size:.72rem;font-weight:800;text-transform:uppercase;letter-spacing:.08em;margin-bottom:2px}.match-tile{width:100%;min-height:54px;border-radius:12px;padding:9px 8px;border:1px solid var(--line);background:linear-gradient(145deg,#341a30,#210f1e);color:var(--ink);font:inherit;font-size:.82rem;font-weight:750;line-height:1.22;cursor:pointer;box-shadow:0 5px 14px rgba(0,0,0,.14);transition:transform .15s ease,border-color .15s ease,background .15s ease,opacity .15s ease}.match-left-tile.is-selected{border-color:#e0227f;box-shadow:0 0 0 2px rgba(224,34,127,.22),0 7px 18px rgba(0,0,0,.2);transform:translateX(2px)}.match-right-tile{font-size:.76rem;min-height:58px;background:linear-gradient(145deg,#3a1a3a,#25102a);color:var(--ink);font-weight:650}.match-right-tile.is-open{border-color:#e0227f;color:var(--ink)}.match-right-tile.is-matched,.match-left-tile.is-matched{border-color:#18e58a;background:rgba(3,91,56,.28);color:#b9ffdf;opacity:.72;cursor:default}.match-right-tile:disabled,.match-left-tile:disabled{cursor:default}.match-win{margin:14px 0;padding:12px;border:1px solid #1b9364;border-radius:12px;background:rgba(3,91,56,.25);text-align:center;color:#b9ffdf;font-weight:750}@media(max-width:600px){.match-grid{gap:8px}.match-column{gap:7px}.match-tile{min-height:52px;padding:8px 6px;font-size:.72rem}.match-right-tile{font-size:.76rem}.match-head{align-items:flex-start}.match-head h2{font-size:1.15rem}.match-head .next-btn{padding:8px 10px;font-size:.76rem}}


/* ============================================================
   EXPANDED CARD VIEW
   ============================================================ */
.expand-card-btn,.pair-expand-btn{
  position:relative;z-index:8;border:1px solid rgba(255,122,184,.45);border-radius:999px;
  padding:7px 11px;background:rgba(20,9,16,.72);color:#ff9bc7;font:inherit;font-size:.72rem;font-weight:800;
  cursor:pointer;box-shadow:0 4px 12px rgba(0,0,0,.2)
}
.expand-card-btn{margin-top:10px}
.expand-card-btn:hover,.pair-expand-btn:hover{border-color:#e0227f;background:rgba(224,34,127,.16)}
.expand-modal{position:fixed;inset:0;z-index:100;display:flex;align-items:center;justify-content:center;padding:18px;background:rgba(8,3,7,.82);backdrop-filter:blur(10px);-webkit-backdrop-filter:blur(10px)}
.expand-dialog{position:relative;width:min(720px,100%);max-height:min(88vh,760px);overflow:auto;border:1px solid #8a3468;border-radius:26px;padding:30px;background:radial-gradient(circle at 80% 5%,rgba(224,34,127,.14),transparent 30%),linear-gradient(145deg,#3a1a34,#170b1c);box-shadow:0 30px 80px rgba(0,0,0,.6);text-align:center;color:var(--ink)}
.expand-dialog h2{margin:14px 38px 18px;font-size:clamp(1.35rem,4vw,2rem)}
.expand-content{font-size:1rem;line-height:1.55}
.expand-formula{font-size:clamp(1.1rem,3vw,1.6rem);margin:8px 0 20px}
.expand-prompt{font-size:1.15rem;font-weight:750}
.expand-dialog .desc{max-width:620px;margin:0 auto 14px;font-size:1rem;line-height:1.6}
.expand-dialog .tip-line{font-size:.9rem;color:var(--pink-soft)}
.expand-close{position:absolute;top:12px;right:14px;width:38px;height:38px;border:1px solid var(--line);border-radius:50%;background:#241220;color:var(--ink);font-size:1.6rem;line-height:1;cursor:pointer}
.expand-close-btn{margin-top:18px}

/* Paires: keep cards compact in the grid, but make their content readable and expandable. */
.pair-tile{overflow:visible}
.pair-content{padding:9px 7px}
.pair-actions{display:block;margin-top:4px}
.pair-tile{position:relative}.pair-expand-btn{position:absolute;top:7px;right:7px;width:30px;height:30px;padding:0;display:flex;align-items:center;justify-content:center;font-size:1rem;line-height:1;border-radius:50%;background:rgba(20,9,16,.8)}
.pair-tile:focus-visible{outline:2px solid var(--pink);outline-offset:2px;border-radius:15px}

/* Relier: visible right-hand targets; support click selection and desktop drag/drop. */
.match-left-tile{cursor:grab}
.match-left-tile.is-dragging{opacity:.55}
.match-right-tile{cursor:pointer}
.match-right-tile.is-drop-target{border-color:#e0227f;box-shadow:0 0 0 2px rgba(224,34,127,.22),0 8px 20px rgba(0,0,0,.22);transform:scale(1.02)}

@media(max-width:600px){
  .expand-modal{padding:10px}
  .expand-dialog{max-height:92vh;padding:24px 16px;border-radius:20px}
  .expand-dialog h2{margin-left:28px;margin-right:28px}
  .pair-expand-btn{top:5px;right:5px;width:27px;height:27px;font-size:.88rem}
}