*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --bg: #0f0f0f;
  --surface: #161616;
  --surface2: #1e1e1e;
  --border: #353535;
  --text: #e8e8e8;
  --muted: #666;
  --accent: #3cb371;
  --accent-hover: #2e9e5e;
  --good: #3d9e6b;
  --again: #c0392b;
  --radius: 10px;
  --font: 'Inter', 'Segoe UI', system-ui, sans-serif;
}

body {
  font-family: var(--font);
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  height: 100vh;
  display: flex;
  justify-content: center;
  overflow: hidden;
}

#page-layout {
  display: grid;
  grid-template-columns: 160px minmax(0, 560px) 160px;
  gap: 0 24px;
  justify-content: center;
  align-items: start;
  width: 100%;
  max-width: 1060px;
  padding: 0 16px;
  box-sizing: border-box;
  height: 100vh;
}

#ad-sidebar {
  grid-column: 3;
  grid-row: 1;
  width: 160px;
  position: sticky;
  top: 20px;
  padding-top: 20px;
  background: #1e1e1e;
  border: 1px dashed #353535;
  border-radius: var(--radius);
  min-height: 600px;
  display: flex;
  align-items: flex-start;
  justify-content: center;
  padding: 20px 8px 8px;
  color: #444;
  font-size: 0.72rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  position: relative;
}
#ad-sidebar::before {
  content: 'Ad';
  position: absolute;
  top: 12px;
  left: 50%;
  transform: translateX(-50%);
  pointer-events: none;
}

.ad-banner-study {
  width: 100%;
  margin-top: 24px;
  text-align: center;
  background: #1e1e1e;
  border: 1px dashed #353535;
  border-radius: var(--radius);
  min-height: 90px;
  display: flex;
  align-items: center;
  justify-content: center;
  color: #444;
  font-size: 0.72rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  position: relative;
}
.ad-banner-study::before {
  content: 'Advertisement';
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  pointer-events: none;
}

.ad-banner-modal {
  width: 100%;
  margin-top: 16px;
  text-align: center;
  background: #1e1e1e;
  border: 1px dashed #353535;
  border-radius: var(--radius);
  min-height: 90px;
  display: flex;
  align-items: center;
  justify-content: center;
  color: #444;
  font-size: 0.72rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  position: relative;
}
.ad-banner-modal::before {
  content: 'Advertisement';
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  pointer-events: none;
}

@media (max-width: 860px) {
  body {
    overflow: hidden;
    justify-content: flex-start;
  }
  #page-layout {
    display: flex;
    flex-direction: column;
    width: 100%;
    max-width: 100%;
    padding: 0 12px;
    height: 100vh;
    box-sizing: border-box;
  }
  .view {
    grid-column: unset;
    width: 100%;
    max-width: 100%;
  }
  #ad-sidebar { display: none; }
}

.view {
  display: none;
  flex-direction: column;
  grid-column: 2;
  width: 100%;
  min-width: 0;
  height: 100vh;
  padding-bottom: 0;
}
.view.active { display: flex; }

/* Header */
header {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 20px 0 16px;
  border-bottom: 1px solid var(--border);
  margin-bottom: 20px;
}
header h1, header h2 {
  flex: 1;
  font-size: 1.25rem;
  font-weight: 800;
}
header h1 { 
  letter-spacing: -0.5px;
  background: linear-gradient(135deg, #5dd68a 0%, #3cb371 60%, #267a4e 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

button {
  font-family: var(--font);
  cursor: pointer;
  border: none;
  border-radius: var(--radius);
  font-size: 0.875rem;
  font-weight: 500;
  padding: 8px 14px;
  transition: background 0.15s, transform 0.1s;
}
button:active { transform: scale(0.97); }

button.back {
  background: none;
  color: var(--accent);
  font-size: 1.25rem;
  padding: 4px 8px;
  border-radius: 6px;
}
button.back:hover { background: var(--surface2); }

#btn-new-deck, #btn-study {
  background: var(--accent);
  color: #fff;
}
#btn-new-deck:hover, #btn-study:hover { background: var(--accent-hover); }

#btn-export {
  background: var(--surface2);
  color: var(--text);
  border: 1px solid var(--border);
  font-size: 0.8rem;
  padding: 7px 12px;
}
#btn-export:hover { background: var(--border); }

/* Deck list */
#deck-list {
  display: flex;
  flex-direction: column;
  gap: 6px;
  flex: 1;
  overflow-y: auto;
  padding-bottom: 8px;
  /* scrollbar styling */
  scrollbar-width: thin;
  scrollbar-color: var(--border) transparent;
}

/* ── Folder ── */
.folder-block { display: flex; flex-direction: column; }

.folder-header {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 8px 10px;
  border-radius: var(--radius);
  background: var(--surface2);
  border: 1px solid var(--border);
  cursor: pointer;
  user-select: none;
  transition: background 0.15s;
}
.folder-header:hover { background: #2c2c2c; }
.folder-header.drag-over {
  border-color: var(--accent);
  background: rgba(37,99,235,0.12);
}
.folder-arrow {
  font-size: 0.7rem;
  color: var(--muted);
  transition: transform 0.2s;
  flex-shrink: 0;
}
.folder-arrow.open { transform: rotate(90deg); }
.folder-icon { font-size: 1rem; flex-shrink: 0; }
.folder-name { flex: 1; font-size: 0.9rem; font-weight: 800; }
.folder-meta { font-size: 0.75rem; color: var(--muted); flex-shrink: 0; }
.folder-actions { display: flex; gap: 4px; flex-shrink: 0; }
.folder-actions button {
  background: none;
  color: var(--muted);
  padding: 2px 6px;
  border-radius: 5px;
  font-size: 0.78rem;
}
.folder-actions button:hover { background: var(--border); color: var(--text); }

.folder-children {
  display: flex;
  flex-direction: column;
  gap: 4px;
  margin-left: 18px;
  margin-top: 4px;
  padding: 4px 6px 6px;
  border-left: 2px solid var(--border);
  border-radius: 0 0 0 6px;
  min-height: 36px;
}
/* Nested folder blocks inside a parent get a subtle extra indent */
.folder-children > .folder-block { margin-left: 0; }
.folder-children.collapsed { display: none; }
.folder-children.drag-over {
  border-left-color: var(--accent);
  background: rgba(37,99,235,0.06);
  border-radius: 6px;
}
.folder-empty {
  font-size: 0.78rem;
  color: var(--muted);
  padding: 4px 2px;
  pointer-events: none;
}

/* Root drop zone */
#root-drop-zone {
  min-height: 32px;
  border-radius: var(--radius);
  border: 2px dashed transparent;
  transition: border-color 0.15s, background 0.15s;
  margin-top: 4px;
}
#root-drop-zone.drag-over {
  border-color: var(--accent);
  background: rgba(37,99,235,0.06);
}

.deck-item {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 14px 16px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  cursor: grab;
  transition: background 0.15s, opacity 0.15s, box-shadow 0.15s;
}
.deck-item:hover { background: var(--surface2); }
.deck-item.dragging { opacity: 0.35; cursor: grabbing; }
/* Touch-drag long-press feedback */
.deck-item:active    { background: var(--surface2); }
.deck-item .deck-name {
  font-size: 1rem;
  font-weight: 700;
  min-width: 0;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}
.deck-item .deck-meta {
  font-size: 0.78rem;
  color: var(--muted);
  margin-top: 2px;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}
.deck-actions {
  display: flex;
  gap: 6px;
  flex-shrink: 0;
}
.deck-actions button, .card-actions button {
  background: none;
  color: var(--muted);
  padding: 4px 8px;
  border-radius: 6px;
  font-size: 0.8rem;
}
.deck-actions button:hover, .card-actions button:hover {
  background: var(--surface2);
  color: var(--text);
}

/* Card list */
#card-list {
  display: flex;
  flex-direction: column;
  gap: 8px;
  flex: 1;
  overflow-y: auto;
  padding-bottom: 80px;
  scrollbar-width: thin;
  scrollbar-color: var(--border) transparent;
}

.card-item {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 12px 14px;
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
}
.card-item .card-texts { flex: 1; min-width: 0; }
.card-item .card-q {
  font-size: 0.9rem;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}
.card-item .card-a {
  font-size: 0.78rem;
  color: var(--muted);
  margin-top: 2px;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}
.card-actions { display: flex; gap: 4px; flex-shrink: 0; }

/* Per-card rating stats */
.card-stats {
  display: flex;
  gap: 6px;
  margin-top: 5px;
}
.card-stat {
  font-size: 0.72rem;
  font-weight: 700;
  border-radius: 4px;
  padding: 1px 5px;
  cursor: default;
  user-select: none;
}
.stat-difficult { color: #e74c3c; background: rgba(231,76,60,0.12); }
.stat-hard      { color: #e67e22; background: rgba(230,126,34,0.12); }
.stat-easy      { color: #27ae60; background: rgba(39,174,96,0.12);  }
.stat-light     { color: #2980b9; background: rgba(41,128,185,0.12); }

/* Deck size bar */
#deck-size-bar {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 6px 0 2px;
  margin-bottom: 2px;
}
#deck-size-fill {
  height: 4px;
  border-radius: 4px;
  background: var(--accent);
  transition: width 0.3s, background 0.3s;
  min-width: 2px;
}
#deck-size-label {
  font-size: 0.72rem;
  color: var(--muted);
  white-space: nowrap;
}
#deck-size-bar.warn #deck-size-fill  { background: #e67e22; }
#deck-size-bar.danger #deck-size-fill { background: #c0392b; }
#deck-size-bar.warn  #deck-size-label { color: #e67e22; }
#deck-size-bar.danger #deck-size-label { color: #c0392b; }

/* FAB */
.fab {
  position: fixed;
  bottom: 24px;
  right: calc(50% - 280px + 16px);
  background: var(--accent);
  color: #fff;
  padding: 12px 20px;
  border-radius: 50px;
  font-size: 0.9rem;
  box-shadow: 0 4px 16px rgba(37,99,235,0.35);
  z-index: 10;
}
.fab:hover { background: var(--accent-hover); }
/* Swipe-to-delete button (revealed by touch swipe left, hidden on desktop) */
.swipe-delete-btn {
  position: absolute;
  right: -80px;
  top: 0;
  bottom: 0;
  width: 80px;
  background: #c0392b;
  color: #fff;
  border: none;
  border-radius: 0 var(--radius) var(--radius) 0;
  font-size: 0.82rem;
  font-weight: 700;
  cursor: pointer;
  display: none; /* hidden on desktop; shown only on mobile */
  align-items: center;
  justify-content: center;
  z-index: 2;
}
.swipe-delete-btn:hover { background: #a93226; }

/* Folder dragging state */
.folder-block.dragging { opacity: 0.35; }

/* Desktop-only delete button — hidden on mobile via media query */
.btn-delete-desktop { display: inline-flex; }

@media (max-width: 600px) { .fab { right: 16px; } }

/* 3D Flip Card */
#study-area {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 20px;
  padding-top: 24px;
}

.card-3d {
  width: 100%;
  max-width: 480px;
  height: 240px;
  perspective: 1200px;
  cursor: pointer;
  position: relative;
}
.card-3d.flipped .card-face.front { transform: rotateY(-180deg); }
.card-3d.flipped .card-face.back  { transform: rotateY(0deg); }

.card-face {
  width: 100%;
  height: 100%;
  border-radius: 14px;
  background: var(--surface);
  border: 1px solid var(--border);
  backface-visibility: hidden;
  position: absolute;
  transition: transform 0.45s cubic-bezier(0.4,0,0.2,1);
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  padding: 24px;
  text-align: center;
}
.card-face.front { transform: rotateY(0deg); }
.card-face.back  { transform: rotateY(180deg); }
.card-face p { font-size: 1.15rem; line-height: 1.5; }

#rating-btns {
  display: flex;
  gap: 8px;
  margin-top: 20px;
  flex-wrap: wrap;
  justify-content: center;
}
.rating {
  padding: 8px 18px;
  border-radius: 50px;
  font-size: 0.8rem;
  font-weight: 700;
  color: #fff;
  flex: 1 1 auto;
  min-width: 80px;
}
.rating.difficult { background: #c0392b; }
.rating.hard      { background: #d35400; }
.rating.easy      { background: #2980b9; }
.rating.light     { background: var(--good); }
.rating:hover { filter: brightness(1.15); }

.flip-btn {
  background: var(--surface2);
  color: var(--text);
  border: 1px solid var(--border);
  padding: 10px 32px;
  border-radius: 50px;
  font-size: 0.9rem;
}
.flip-btn:hover { background: var(--border); }

#study-progress {
  flex: 1;
  text-align: center;
  font-size: 1.05rem;
  font-weight: 800;
  color: #e8621a;
  text-shadow: none;
  letter-spacing: -0.2px;
}

#study-done {
  margin-top: 80px;
  text-align: center;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 20px;
}
#study-done p { font-size: 1.2rem; color: var(--muted); }
#btn-finish-study {
  background: var(--accent);
  color: #fff;
  padding: 10px 28px;
}

/* Modal */
#modal-overlay {
  position: fixed; inset: 0;
  background: rgba(0,0,0,0.65);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 100;
  padding: 16px;
}
#modal {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 24px;
  width: 100%;
  max-width: 420px;
  display: flex;
  flex-direction: column;
  gap: 14px;
}
#modal h3 { font-size: 1rem; font-weight: 800; }

#modal input {
  font-family: var(--font);
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text);
  font-size: 0.9rem;
  padding: 10px 12px;
  width: 100%;
  outline: none;
}
#modal input:focus { border-color: var(--accent); }

/* Card contenteditable fields */
.card-field-row {
  display: flex;
  align-items: flex-start;
  gap: 6px;
}
.modal-field {
  flex: 1;
  font-family: var(--font);
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text);
  font-size: 0.9rem;
  padding: 10px 12px;
  min-height: 64px;
  max-height: 160px;
  overflow-y: auto;
  outline: none;
  line-height: 1.5;
  word-break: break-word;
}
.modal-field:focus { border-color: var(--accent); }
.modal-field:empty::before {
  content: attr(data-placeholder);
  color: var(--muted);
  pointer-events: none;
}
.modal-field img {
  max-width: 100%;
  max-height: 120px;
  border-radius: 4px;
  display: block;
  margin: 4px 0;
  transition: opacity 0.2s;
}
/* Spinner overlay while image is uploading to Firebase Storage */
.modal-field img.img-uploading {
  opacity: 0.35;
  position: relative;
  outline: 2px dashed var(--accent);
  outline-offset: 2px;
}
.img-pick-btn {
  background: var(--surface2);
  border: 1px solid var(--border);
  color: var(--text);
  padding: 6px 8px;
  border-radius: 8px;
  font-size: 1rem;
  flex-shrink: 0;
  margin-top: 2px;
}
.img-pick-btn:hover { background: var(--border); }

/* Card added toast */
.card-toast {
  font-size: 0.82rem;
  color: var(--good);
  text-align: center;
  padding: 4px 0;
}

/* Global rate-limit toast */
#global-toast {
  position: fixed;
  bottom: 40px;
  left: 50%;
  transform: translateX(-50%) translateY(20px);
  background: #c0392b;
  border: none;
  color: #fff;
  font-size: 1rem;
  font-weight: 600;
  padding: 16px 32px;
  border-radius: 14px;
  box-shadow: 0 6px 28px rgba(0,0,0,0.6);
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.2s, transform 0.2s;
  white-space: nowrap;
  z-index: 9999;
}
#global-toast.visible {
  opacity: 1;
  transform: translateX(-50%) translateY(0);
}

/* Card type toggle */
#card-type-toggle {
  display: flex;
  gap: 6px;
}
.type-btn {
  flex: 1;
  padding: 7px 0;
  border-radius: 8px;
  font-size: 0.85rem;
  font-weight: 700;
  background: var(--surface2);
  border: 1px solid var(--border);
  color: var(--muted);
}
.type-btn.active {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
}
.type-btn:hover:not(.active) { background: var(--border); color: var(--text); }

/* Cloze field */
.cloze-toolbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 6px;
  gap: 8px;
}
.cloze-hint { font-size: 0.78rem; color: var(--muted); }
.cloze-hint strong { color: var(--text); }
.cloze-wrap-btn {
  background: var(--surface2);
  border: 1px solid var(--border);
  color: var(--text);
  padding: 5px 10px;
  border-radius: 6px;
  font-size: 0.82rem;
  font-weight: 700;
  flex-shrink: 0;
}
.cloze-wrap-btn:hover { background: var(--border); }
.cloze-field { min-height: 80px; }

/* Cloze blanks in study */
.cloze-blank {
  display: inline-block;
  background: #0d0d0d;
  color: transparent;
  border-radius: 5px;
  padding: 2px 12px;
  min-width: 52px;
  user-select: none;
  vertical-align: middle;
  border: 1.5px solid #3a3a3a;
  box-shadow: inset 0 1px 3px rgba(0,0,0,0.5);
}
.cloze-answer {
  display: inline;
  color: #e8621a;
  font-weight: 700;
}

/* Cloze badge in card list */
.badge-cloze {
  font-size: 0.68rem;
  font-weight: 700;
  background: rgba(37,99,235,0.2);
  color: var(--accent);
  border: 1px solid var(--accent);
  border-radius: 4px;
  padding: 1px 5px;
  margin-right: 5px;
  vertical-align: middle;
}

/* Images inside study cards */
.card-content {
  width: 100%;
  overflow: auto;
  text-align: center;
  line-height: 1.5;
}
.card-content img {
  max-width: 100%;
  max-height: 130px;
  border-radius: 6px;
  display: block;
  margin: 4px auto;
}

/* Back-of-card Q+A layout */
.back-question {
  font-size: 0.78rem;
  color: var(--muted);
  margin-bottom: 4px;
  line-height: 1.4;
}
.back-divider {
  width: 40px;
  height: 2px;
  background: var(--border);
  border-radius: 2px;
  margin: 6px auto;
}
.back-answer {
  font-size: 1rem;
  font-weight: 600;
  line-height: 1.5;
}

.modal-actions {
  display: flex;
  justify-content: flex-end;
  gap: 10px;
}
#modal-cancel {
  background: none;
  color: var(--muted);
  border: 1px solid var(--border);
}
#modal-cancel:hover { background: var(--surface2); }
button.primary {
  background: var(--accent);
  color: #fff;
}
button.primary:hover { background: var(--accent-hover); }

/* Confetti canvas */
#confetti-canvas {
  position: absolute;
  inset: 0;
  border-radius: 14px;
  pointer-events: none;
  z-index: 20;
}

/* Stats bar */
#home-stats {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0;
  margin-top: auto;
  padding: 12px 0 20px;
  border-top: 1px solid var(--border);
}
.stat-item {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 3px;
  padding: 0 28px;
}
.stat-value {
  font-size: 1.3rem;
  font-weight: 800;
  color: var(--text);
  letter-spacing: -0.5px;
}
.stat-label {
  font-size: 0.72rem;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 0.04em;
}
.stat-divider {
  width: 1px;
  height: 32px;
  background: var(--border);
}

.muted { color: var(--muted); font-size: 0.875rem; margin-top: 12px; }
.app-description {
  margin-top: 16px;
  padding: 14px 16px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  color: var(--muted);
  font-size: 0.8rem;
  line-height: 1.6;
  text-align: center;
}
.app-description strong { color: var(--text); }

/* ─── Math rendering ───────────────────────────────────────────────────── */
/* Fraction */
.math-frac {
  display: inline-flex;
  flex-direction: column;
  align-items: center;
  vertical-align: middle;
  margin: 0 3px;
  line-height: 1.2;
}
.math-num {
  border-bottom: 1.5px solid currentColor;
  padding: 1px 5px;
  font-size: 0.82em;
  text-align: center;
}
.math-den {
  padding: 1px 5px;
  font-size: 0.82em;
  text-align: center;
}

/* Summation */
.math-sum {
  display: inline-grid;
  grid-template-columns: auto;
  grid-template-rows: auto auto auto;
  align-items: center;
  vertical-align: middle;
  margin: 0 2px;
}
.math-top {
  grid-row: 1;
  font-size: 0.62em;
  text-align: center;
  color: var(--muted);
  line-height: 1.2;
}
.math-sigma {
  grid-row: 2;
  font-size: 1.5em;
  line-height: 1;
  text-align: center;
}
.math-bot {
  grid-row: 3;
  font-size: 0.62em;
  text-align: center;
  color: var(--muted);
  line-height: 1.2;
}
.math-sum-expr {
  display: inline-block;
  vertical-align: middle;
  margin-left: 3px;
}

/* Square root */
.math-sqrt {
  display: inline;
  font-size: 1.05em;
}
.math-sqrt-inner {
  border-top: 1.5px solid currentColor;
  padding: 1px 4px 1px 2px;
  margin-left: 1px;
  font-size: 0.9em;
}

/* Live math preview below input fields */
.math-preview {
  display: none;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 6px 12px;
  font-size: 0.9rem;
  color: var(--text);
  margin-bottom: 8px;
  min-height: 34px;
  line-height: 1.6;
}
.math-preview.has-content { display: block; }

/* Math tips button */
.math-tips-btn {
  background: none;
  border: 1px solid var(--border);
  color: var(--muted);
  font-size: 0.75rem;
  padding: 4px 10px;
  border-radius: 6px;
  cursor: pointer;
  margin-top: 10px;
  width: 100%;
  text-align: left;
}
.math-tips-btn:hover { background: var(--surface2); color: var(--text); }

/* Math tips panel */
#math-tips-panel {
  display: none;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 10px 12px;
  margin-top: 6px;
  font-size: 0.78rem;
}
#math-tips-panel.open { display: block; }
#math-tips-panel table { width: 100%; border-collapse: collapse; }
#math-tips-panel td {
  padding: 4px 6px;
  border-bottom: 1px solid var(--border);
  vertical-align: middle;
}
#math-tips-panel td:first-child {
  font-family: 'Courier New', monospace;
  color: var(--accent);
  white-space: nowrap;
  width: 40%;
}
#math-tips-panel tr:last-child td { border-bottom: none; }

/* ── Tags ────────────────────────────────────────────────────────────────────*/
#row-tags { display: flex; flex-direction: column; gap: 6px; }
#tag-chips { display: flex; flex-wrap: wrap; gap: 5px; min-height: 0; }
.tag-chip {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  background: rgba(74,144,217,0.15);
  color: #4a90d9;
  border: 1px solid rgba(74,144,217,0.3);
  border-radius: 20px;
  padding: 2px 9px 2px 10px;
  font-size: 0.75rem;
  font-weight: 700;
}
.tag-chip .tag-remove {
  cursor: pointer;
  font-size: 0.7rem;
  opacity: 0.65;
  line-height: 1;
  padding: 0 1px;
}
.tag-chip .tag-remove:hover { opacity: 1; }
.tag-input-row {
  display: flex;
  gap: 6px;
  align-items: center;
}
.tag-input-row input {
  font-family: var(--font);
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text);
  font-size: 0.85rem;
  padding: 6px 10px;
  flex: 1;
  outline: none;
}
.tag-input-row input:focus { border-color: var(--accent); }
.tag-add-btn {
  background: var(--surface2);
  border: 1px solid var(--border);
  color: var(--text);
  font-size: 0.82rem;
  font-weight: 700;
  padding: 6px 12px;
  border-radius: 8px;
  flex-shrink: 0;
}
.tag-add-btn:hover { background: var(--border); }

/* Inline tags on card list item */
.card-tags { display: flex; flex-wrap: wrap; gap: 4px; margin-top: 4px; }
.card-tag {
  font-size: 0.65rem;
  font-weight: 700;
  background: rgba(74,144,217,0.12);
  color: #4a90d9;
  border-radius: 20px;
  padding: 1px 7px;
  border: 1px solid rgba(74,144,217,0.25);
}

/* Tag filter bar in deck view */
#tag-filter-bar {
  display: flex;
  align-items: center;
  gap: 8px;
  flex-wrap: wrap;
  padding: 8px 12px;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  margin-bottom: 10px;
}
.tag-filter-label {
  font-size: 0.72rem;
  font-weight: 700;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 0.04em;
  flex-shrink: 0;
}
#tag-filter-chips { display: flex; flex-wrap: wrap; gap: 5px; flex: 1; }
.tag-filter-chip {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  background: var(--surface);
  border: 1.5px solid var(--border);
  border-radius: 20px;
  padding: 3px 11px;
  font-size: 0.75rem;
  font-weight: 700;
  color: var(--muted);
  cursor: pointer;
  transition: border-color 0.12s, color 0.12s, background 0.12s;
  user-select: none;
}
.tag-filter-chip.active {
  border-color: #4a90d9;
  color: #4a90d9;
  background: rgba(74,144,217,0.12);
}
.tag-clear-btn {
  background: none;
  color: var(--muted);
  font-size: 0.75rem;
  padding: 3px 8px;
  border-radius: 6px;
  flex-shrink: 0;
}
.tag-clear-btn:hover { background: var(--border); color: var(--text); }

/* ── Bulk-tag bar ────────────────────────────────────────────────────────────*/
#bulk-tag-bar {
  display: flex;
  align-items: center;
  gap: 8px;
  flex-wrap: wrap;
  padding: 8px 12px;
  background: #1a2a1a;
  border: 1px solid var(--accent);
  border-radius: var(--radius);
  margin-bottom: 10px;
}
#bulk-tag-bar.hidden { display: none; }
.bulk-tag-count {
  font-size: 0.75rem;
  font-weight: 700;
  color: var(--accent);
  flex-shrink: 0;
  white-space: nowrap;
}
#bulk-tag-input {
  flex: 1;
  min-width: 120px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 6px;
  color: var(--text);
  font-size: 0.85rem;
  padding: 5px 10px;
  font-family: var(--font);
}
#bulk-tag-input:focus { outline: none; border-color: var(--accent); }
.bulk-apply-btn {
  background: var(--accent);
  color: #fff;
  font-size: 0.8rem;
  padding: 5px 12px;
  border-radius: 6px;
  flex-shrink: 0;
}
.bulk-apply-btn:hover { background: var(--accent-hover); }
.bulk-deselect-btn {
  background: var(--surface2);
  color: var(--muted);
  font-size: 0.8rem;
  padding: 5px 10px;
  border-radius: 6px;
  border: 1px solid var(--border);
  flex-shrink: 0;
}
.bulk-deselect-btn:hover { background: var(--border); color: var(--text); }
.bulk-cancel-btn {
  background: none;
  color: var(--muted);
  font-size: 0.8rem;
  padding: 5px 10px;
  border-radius: 6px;
  flex-shrink: 0;
}
.bulk-cancel-btn:hover { background: var(--border); color: var(--text); }
.bulk-remove-btn {
  background: rgba(231,76,60,0.1);
  color: #e74c3c;
  font-size: 0.8rem;
  padding: 5px 12px;
  border-radius: 6px;
  border: 1px solid rgba(231,76,60,0.25);
  flex-shrink: 0;
}
.bulk-remove-btn:hover { background: rgba(231,76,60,0.22); }
.bulk-select-all-btn {
  background: var(--surface2);
  color: var(--muted);
  font-size: 0.8rem;
  padding: 5px 10px;
  border-radius: 6px;
  border: 1px solid var(--border);
  flex-shrink: 0;
}
.bulk-select-all-btn:hover { background: var(--border); color: var(--text); }

/* ── Code blocks ─────────────────────────────────────────────────────────────*/
.code-block {
  background: #0d0d0d;
  border: 1px solid #2a2a2a;
  border-radius: 8px;
  margin: 6px 0;
  overflow: hidden;
  display: block;
}
.code-block-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 4px 10px;
  background: #161616;
  border-bottom: 1px solid #2a2a2a;
}
.code-lang-badge {
  font-size: 0.68rem;
  font-weight: 700;
  color: var(--accent);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  font-family: var(--font);
}
.code-block-del {
  background: none;
  border: none;
  color: #444;
  font-size: 1rem;
  cursor: pointer;
  padding: 0 3px;
  border-radius: 4px;
  line-height: 1;
  transition: color 0.12s, background 0.12s;
}
.code-block-del:hover { color: #e74c3c; background: rgba(231,76,60,0.12); }

/* Textarea for editing code */
.code-textarea {
  display: block;
  width: 100%;
  min-height: 72px;
  padding: 10px 14px;
  background: #0d0d0d;
  color: #d4d4d4;
  border: none;
  outline: none;
  resize: none;
  font-family: 'Fira Code', 'Cascadia Code', 'Courier New', monospace;
  font-size: 0.82rem;
  line-height: 1.55;
  tab-size: 4;
  white-space: pre;
  overflow-wrap: normal;
  overflow-x: auto;
  box-sizing: border-box;
  caret-color: var(--accent);
}
.code-textarea::placeholder { color: #333; }

/* Prism pre/code inside code blocks */
.code-block pre[class*="language-"] {
  margin: 0;
  padding: 10px 14px;
  background: #0d0d0d !important;
  border-radius: 0;
  font-size: 0.82rem;
  line-height: 1.55;
  cursor: text;
}
.code-block pre[class*="language-"] code {
  background: none !important;
  padding: 0;
  font-size: inherit;
  line-height: inherit;
  white-space: pre-wrap;
  word-break: break-all;
}
/* Display mode (study card) */
.card-content .code-block pre[class*="language-"] { cursor: default; }

/* ── Card item selection mode ────────────────────────────────────────────────*/
#btn-select-mode {
  background: var(--surface2);
  color: var(--muted);
  border: 1px solid var(--border);
  font-size: 0.8rem;
  padding: 7px 12px;
}
#btn-select-mode:hover { background: var(--border); color: var(--text); }
#btn-select-mode.active {
  background: rgba(60,179,113,0.15);
  color: var(--accent);
  border-color: var(--accent);
}

.card-item.selectable { cursor: pointer; user-select: none; }
.card-item.selectable:hover { border-color: #4a90d9; }
.card-item.selected {
  border-color: var(--accent);
  background: rgba(60,179,113,0.08);
}
.card-select-cb {
  width: 18px;
  height: 18px;
  flex-shrink: 0;
  border: 2px solid var(--border);
  border-radius: 5px;
  margin-right: 10px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.75rem;
  color: #fff;
  transition: background 0.12s, border-color 0.12s;
}
.card-item.selected .card-select-cb {
  background: var(--accent);
  border-color: var(--accent);
}

/* ── Auth overlay ────────────────────────────────────────────────────────────*/
#auth-overlay {
  position: fixed; inset: 0;
  background: var(--bg);
  z-index: 200;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 20px;
}
#auth-modal {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 14px;
  max-width: 340px;
  width: 100%;
  text-align: center;
}
.auth-logo { font-size: 3.5rem; }
#auth-modal h2 {
  font-size: 1.6rem;
  font-weight: 800;
  background: linear-gradient(135deg, #4a90d9, #1e5fa8, #163d75);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}
.auth-subtitle { color: var(--muted); font-size: 0.9rem; }
.google-signin-btn {
  display: flex;
  align-items: center;
  gap: 10px;
  background: #fff;
  color: #3c4043;
  border: 1px solid #dadce0;
  border-radius: 8px;
  padding: 10px 24px;
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  transition: box-shadow 0.15s;
  width: 100%;
  justify-content: center;
}
.google-signin-btn:hover { box-shadow: 0 2px 10px rgba(0,0,0,0.2); }
.auth-note { font-size: 0.72rem; color: var(--muted); }

/* Sync status + sign-out in header */
.sync-status {
  font-size: 0.72rem;
  color: var(--muted);
  font-weight: 600;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  max-width: 80px;
}
.signout-btn {
  background: none;
  color: var(--muted);
  font-size: 1rem;
  padding: 4px 6px;
  border-radius: 6px;
  flex-shrink: 0;
}
.signout-btn:hover { background: var(--surface2); color: var(--text); }

.upgrade-btn {
  background: linear-gradient(135deg, #f6c90e, #f0a500);
  color: #1a1a1a;
  font-size: 0.75rem;
  font-weight: 700;
  padding: 4px 10px;
  border-radius: 20px;
  border: none;
  cursor: pointer;
  flex-shrink: 0;
  letter-spacing: 0.02em;
}
.upgrade-btn:hover { opacity: 0.9; }

.hidden { display: none !important; }

/* ── Import overlay ─────────────────────────────────────────────── */
#import-overlay {
  position: fixed; inset: 0;
  background: rgba(0,0,0,0.65);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 100;
  padding: 16px;
}
#import-modal {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 24px;
  width: 100%;
  max-width: 560px;
  display: flex;
  flex-direction: column;
  gap: 14px;
  max-height: 90vh;
  overflow-y: auto;
}
#import-modal h3 { font-size: 1rem; font-weight: 800; }
.import-hint {
  font-size: 0.82rem;
  color: var(--muted);
  line-height: 1.5;
  margin: 0;
}
.import-hint code {
  background: var(--surface2);
  border-radius: 4px;
  padding: 1px 5px;
  font-size: 0.8rem;
}
#import-textarea {
  font-family: var(--font);
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text);
  font-size: 0.82rem;
  padding: 12px;
  width: 100%;
  min-height: 180px;
  resize: vertical;
  outline: none;
  line-height: 1.5;
  box-sizing: border-box;
}
#import-textarea:focus { border-color: var(--accent); }
#import-preview {
  font-size: 0.8rem;
  color: var(--muted);
  min-height: 1.2em;
}
.import-img-row {
  display: flex;
  flex-direction: column;
  gap: 6px;
}
.import-img-label {
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--text);
}
.import-img-optional {
  font-weight: 400;
  color: var(--muted);
}
.import-img-hint {
  font-size: 0.78rem;
  color: var(--muted);
}
.import-img-hint code {
  background: var(--surface2);
  border-radius: 4px;
  padding: 1px 5px;
  font-size: 0.76rem;
}
#import-img-base {
  font-family: var(--font);
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text);
  font-size: 0.82rem;
  padding: 9px 12px;
  width: 100%;
  outline: none;
  box-sizing: border-box;
}
#import-img-base:focus { border-color: var(--accent); }

/* ── AI Study Panel ─────────────────────────────────────────────────────────── */
.ai-key-btn {
  background: none;
  color: var(--muted);
  font-size: 1.05rem;
  padding: 4px 6px;
  border-radius: 6px;
  flex-shrink: 0;
  line-height: 1;
}
.ai-key-btn:hover { background: var(--surface2); color: var(--text); }

.ask-ai-btn {
  background: var(--surface2);
  color: var(--text);
  border: 1px solid var(--border);
  padding: 8px 22px;
  border-radius: 50px;
  font-size: 0.85rem;
  font-weight: 600;
  transition: background 0.15s;
}
.ask-ai-btn:hover:not(:disabled) { background: var(--border); }
.ask-ai-btn:disabled { opacity: 0.5; cursor: default; }

#ai-panel {
  width: 100%;
  max-width: 560px;
  margin: 0 auto;
}
#ai-panel-inner {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 16px 18px;
  font-size: 0.88rem;
  line-height: 1.65;
  color: var(--text);
  white-space: pre-wrap;
  word-break: break-word;
}
#ai-response .ai-thinking {
  color: var(--muted);
  font-style: italic;
  font-size: 0.82rem;
}
#ai-response code {
  background: var(--surface2);
  border-radius: 4px;
  padding: 1px 5px;
  font-size: 0.82rem;
  font-family: monospace;
}
#ai-response pre {
  background: var(--surface2);
  border-radius: 8px;
  padding: 10px 12px;
  overflow-x: auto;
  font-size: 0.8rem;
  font-family: monospace;
  line-height: 1.5;
  margin: 6px 0;
}

/* ── Mobile / iPhone ──────────────────────────────────────────────────────── */
@media (max-width: 600px) {
  /* Safe area for notch + home bar */
  .view {
    padding-top: env(safe-area-inset-top);
    padding-left: max(16px, env(safe-area-inset-left));
    padding-right: max(16px, env(safe-area-inset-right));
    padding-bottom: max(80px, calc(64px + env(safe-area-inset-bottom)));
  }

  /* Push header below Dynamic Island / notch */
  header {
    gap: 6px;
    padding-top: max(14px, calc(8px + env(safe-area-inset-top)));
    padding-bottom: 12px;
    flex-wrap: nowrap;
    overflow: hidden;
  }
  header h1, header h2 {
    font-size: 1rem;
    min-width: 0;
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
  }
  header button {
    font-size: 0.78rem;
    padding: 7px 10px;
    flex-shrink: 0;
  }
  header button.back {
    font-size: 1.1rem;
    padding: 4px 6px;
  }

  /* Deck items — bigger tap targets */
  .deck-item { padding: 14px 12px; }
  .deck-item .deck-name { font-size: 0.95rem; }

  /* Card list */
  .card-item { padding: 10px 12px; }

  /* FAB bottom-right with home bar clearance */
  .fab {
    right: 16px;
    bottom: max(20px, calc(16px + env(safe-area-inset-bottom)));
  }

  /* Study card — flexible height instead of fixed */
  .card-3d {
    height: auto;
    min-height: 200px;
  }
  .card-face {
    position: relative;
    min-height: 200px;
    height: auto;
    padding: 20px 16px;
  }
  /* Stacked faces on mobile (no 3D flip — easier to read) */
  .card-3d.flipped .card-face.front { display: none; }
  .card-face.back { transform: none; display: none; }
  .card-3d.flipped .card-face.back  { display: flex; transform: none; }
  .card-face.front { transform: none; backface-visibility: visible; }

  /* Rating buttons — full width rows */
  #rating-btns {
    flex-direction: row;
    flex-wrap: wrap;
    gap: 6px;
  }
  .rating {
    flex: 1 1 calc(50% - 6px);
    min-width: 0;
    padding: 10px 8px;
    font-size: 0.78rem;
  }

  /* Study progress text */
  #study-progress { font-size: 0.82rem; }

  /* AI panel */
  #ai-panel { padding: 0; }
  #ai-panel-inner { font-size: 0.84rem; padding: 12px 14px; }

  /* Import modal textarea */
  #import-textarea { min-height: 140px; }

  /* Use desktop delete buttons on mobile too — no swipe needed */
  .btn-delete-desktop { display: inline-flex !important; }
  .swipe-delete-btn { display: none !important; }

  /* Full-width deck and folder items */
  .deck-item, .folder-header { overflow: hidden; width: 100%; box-sizing: border-box; }

  /* Compact description on mobile so it doesn't eat screen space */
  .app-description {
    font-size: 0.72rem;
    padding: 8px 12px;
    margin-top: 8px;
    line-height: 1.4;
  }

  /* Modal max height so it doesn't overflow screen */
  #modal, #import-modal {
    max-height: 92vh;
    overflow-y: auto;
  }

  /* Auth modal */
  #auth-modal { padding: 32px 20px; }
}