/* ============================================================
 * Embedding-game site stylesheet.
 *
 * Tokens, base reset, shared components, page layouts, and the
 * folded-in board styles all live here. Pages wrap their main
 * content in either .page (centered single-column) or .layout
 * (duel two-column).
 * ============================================================ */

:root {
  /* Color palette */
  --color-bg:              #f8fafc;
  --color-surface:         #ffffff;
  --color-surface-2:       #f1f5f9;
  --color-border:          #e2e8f0;
  --color-border-strong:   #cbd5e1;

  --color-text:            #0f172a;
  --color-text-muted:      #475569;
  --color-text-subtle:     #94a3b8;

  --color-primary:         #4f46e5;
  --color-primary-hover:   #4338ca;
  --color-primary-soft:    #eef2ff;
  --color-primary-soft-2:  #e0e7ff;
  --color-primary-text:    #4338ca;

  --color-success:         #10b981;
  --color-success-soft:    #d1fae5;
  --color-success-soft-2:  #a7f3d0;
  --color-success-text:    #065f46;

  --color-danger:          #ef4444;
  --color-danger-hover:    #dc2626;
  --color-danger-soft:     #fef2f2;
  --color-danger-soft-2:   #fee2e2;
  --color-danger-text:     #b91c1c;

  --color-warn:            #f59e0b;
  --color-warn-2:          #d97706;
  --color-warn-soft:       #fef3c7;
  --color-warn-text:       #92400e;

  --color-orange:          #f97316;

  /* Spacing scale */
  --space-1: 0.25rem;
  --space-2: 0.5rem;
  --space-3: 0.75rem;
  --space-4: 1rem;
  --space-5: 1.5rem;
  --space-6: 2rem;
  --space-7: 3rem;

  /* Radii */
  --radius-sm:   0.375rem;
  --radius-md:   0.5rem;
  --radius-lg:   0.75rem;
  --radius-pill: 9999px;

  /* Shadows */
  --shadow-sm: 0 1px 2px rgb(15 23 42 / 0.06);
  --shadow-md: 0 4px 12px rgb(15 23 42 / 0.08);
  --shadow-lg: 0 12px 32px rgb(15 23 42 / 0.14);

  --touch-min: 44px;
  --font-sans: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --t-fast: 0.15s;
  --t-base: 0.2s;
}

/* ============================================================
 * Reset & base
 * ============================================================ */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { -webkit-text-size-adjust: 100%; }

body {
  font-family: var(--font-sans);
  font-size: 1rem;
  line-height: 1.5;
  color: var(--color-text);
  background: var(--color-bg);
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

h1 {
  font-size: clamp(1.5rem, 4vw, 1.9rem);
  font-weight: 700;
  letter-spacing: -0.01em;
  margin-bottom: var(--space-5);
}
h2 { font-size: 1.25rem; font-weight: 700; }
h3 { font-size: 1rem; font-weight: 600; }

a { color: var(--color-primary); text-decoration: none; }
a:hover { text-decoration: underline; }

button { font-family: inherit; }

:focus-visible {
  outline: 2px solid var(--color-primary);
  outline-offset: 2px;
}

/* ============================================================
 * Page wrappers
 * ============================================================ */
.page {
  position: relative;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  padding: clamp(1rem, 4vw, 2rem);
}

.back { align-self: flex-start; margin-bottom: var(--space-4); }
.back-link { color: var(--color-primary); font-size: 0.95rem; }

.author { color: var(--color-text-muted); font-size: 0.95rem; margin-bottom: var(--space-5); }
.subtitle { color: var(--color-text-muted); font-size: 0.95rem; margin-bottom: var(--space-5); }
.empty { color: var(--color-text-muted); font-size: 1.05rem; }

/* Top-right nav (puzzle list) */
.nav {
  position: absolute;
  top: var(--space-4);
  right: var(--space-5);
  font-size: 0.95rem;
  display: flex;
  align-items: center;
  gap: var(--space-4);
}
.nav a { color: var(--color-primary); }
.nav span { color: var(--color-text-muted); }
.nav form { display: inline; }
.nav button {
  background: none; border: none; color: var(--color-primary);
  font-size: inherit; cursor: pointer; padding: 0;
}
.nav button:hover { text-decoration: underline; }

/* ============================================================
 * Forms
 * ============================================================ */
label { display: block; font-weight: 500; margin-bottom: var(--space-1); color: var(--color-text); }

input[type="text"],
input[type="password"],
input[type="number"],
input[type="email"],
select {
  width: 100%;
  padding: var(--space-2) var(--space-3);
  border: 1px solid var(--color-border-strong);
  border-radius: var(--radius-md);
  font-size: 1rem;
  font-family: inherit;
  color: var(--color-text);
  background: var(--color-surface);
  min-height: var(--touch-min);
  transition: border-color var(--t-fast), box-shadow var(--t-fast);
}
input[type="text"]:focus,
input[type="password"]:focus,
input[type="number"]:focus,
input[type="email"]:focus,
select:focus {
  outline: none;
  border-color: var(--color-primary);
  box-shadow: 0 0 0 3px rgb(79 70 229 / 0.15);
}

input[type="checkbox"] { width: 1.05rem; height: 1.05rem; accent-color: var(--color-primary); }
input[type="range"] { width: 100%; accent-color: var(--color-primary); }

.field {
  display: flex;
  flex-direction: column;
  gap: var(--space-1);
  margin-bottom: var(--space-3);
}
.field label { font-size: 0.9rem; color: var(--color-text-muted); }
.field-row { display: flex; align-items: center; gap: var(--space-2); }

.error, .errors {
  color: var(--color-danger-text);
  background: var(--color-danger-soft);
  padding: var(--space-2) var(--space-3);
  border-radius: var(--radius-md);
  font-size: 0.9rem;
  margin-bottom: var(--space-4);
}
.errors ul { margin-left: var(--space-4); }

/* ============================================================
 * Buttons
 * ============================================================ */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  padding: var(--space-2) var(--space-5);
  border: none;
  border-radius: var(--radius-md);
  font-size: 0.95rem;
  font-weight: 600;
  font-family: inherit;
  min-height: var(--touch-min);
  cursor: pointer;
  text-decoration: none;
  transition: background var(--t-fast), color var(--t-fast), transform var(--t-fast);
}
.btn:hover { text-decoration: none; }
.btn:active:not(:disabled) { transform: scale(0.98); }
.btn:disabled { cursor: default; opacity: 0.6; }

.btn-primary { background: var(--color-primary); color: #fff; }
.btn-primary:hover:not(:disabled) { background: var(--color-primary-hover); }
.btn-primary:disabled { background: var(--color-text-subtle); opacity: 1; }

.btn-secondary { background: var(--color-surface-2); color: var(--color-text-muted); }
.btn-secondary:hover:not(:disabled) { background: var(--color-border); }

.btn-success { background: var(--color-success-soft); color: var(--color-success-text); }
.btn-success:hover:not(:disabled) { background: var(--color-success-soft-2); }

.btn-danger { background: var(--color-danger-soft); color: var(--color-danger-text); }
.btn-danger:hover:not(:disabled) { background: var(--color-danger-soft-2); }

.btn-ghost { background: var(--color-primary-soft); color: var(--color-primary-text); }
.btn-ghost:hover:not(:disabled) { background: var(--color-primary-soft-2); }

.btn-block { width: 100%; }

/* Icon-only square button */
.icon-btn {
  background: none; border: none; color: var(--color-text-subtle);
  font-size: 1.05rem; cursor: pointer;
  width: var(--touch-min); height: var(--touch-min);
  display: inline-flex; align-items: center; justify-content: center;
  border-radius: var(--radius-md);
  text-decoration: none;
  font-family: inherit;
  line-height: 1;
  transition: background var(--t-fast), color var(--t-fast);
}
.edit-btn:hover { color: var(--color-primary); background: var(--color-primary-soft); text-decoration: none; }
.delete-btn { font-size: 1.25rem; }
.delete-btn:hover { color: var(--color-danger); background: var(--color-danger-soft); }
.pin-btn { transform: rotate(45deg); }
.pin-btn:hover { color: #d69e2e; background: #fffbeb; }
.pin-btn.pinned { color: #d69e2e; }

/* ============================================================
 * Cards
 * ============================================================ */
.card {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  padding: var(--space-5);
  box-shadow: var(--shadow-sm);
  margin-bottom: var(--space-4);
}
.card h3 {
  font-size: 0.72rem;
  font-weight: 700;
  color: var(--color-text-muted);
  letter-spacing: 0.08em;
  text-transform: uppercase;
  margin-bottom: var(--space-3);
}
.auth-card { width: 100%; max-width: 380px; padding: var(--space-6); }
.auth-submit { margin-top: var(--space-2); }
.auth-alt { text-align: center; margin-top: var(--space-4); font-size: 0.95rem; }

/* ============================================================
 * Tabs
 * ============================================================ */
.tabs {
  display: flex;
  gap: var(--space-1);
  margin-bottom: var(--space-5);
  background: var(--color-surface-2);
  padding: var(--space-1);
  border-radius: var(--radius-pill);
}
.tab {
  background: transparent;
  border: none;
  padding: var(--space-2) var(--space-5);
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--color-text-muted);
  cursor: pointer;
  border-radius: var(--radius-pill);
  font-family: inherit;
  min-height: 40px;
  transition: background var(--t-fast), color var(--t-fast);
}
.tab.active {
  background: var(--color-surface);
  color: var(--color-text);
  box-shadow: var(--shadow-sm);
}
.tab:not(.active):hover { color: var(--color-text); }

.tab-panel { width: 100%; max-width: 420px; display: none; }
.tab-panel.active { display: block; }

/* ============================================================
 * Toggle (switch)
 * ============================================================ */
.toggle {
  position: relative;
  width: 44px;
  height: 26px;
  flex-shrink: 0;
}
.toggle input { opacity: 0; width: 0; height: 0; }
.toggle-slider {
  position: absolute; inset: 0;
  background: var(--color-border-strong);
  border-radius: 13px;
  cursor: pointer;
  transition: background var(--t-base);
}
.toggle-slider::before {
  content: "";
  position: absolute;
  width: 20px; height: 20px;
  left: 3px; top: 3px;
  background: #fff;
  border-radius: 50%;
  transition: transform var(--t-base);
  box-shadow: 0 1px 3px rgb(0 0 0 / 0.2);
}
.toggle input:checked + .toggle-slider { background: var(--color-primary); }
.toggle input:checked + .toggle-slider::before { transform: translateX(18px); }

.toggle-row {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  margin-bottom: var(--space-5);
  font-size: 0.95rem;
  color: var(--color-text-muted);
}

/* ============================================================
 * Recent-opponent chips
 * ============================================================ */
.recent-opponents {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-1);
  margin-top: var(--space-2);
}
.recent-label { font-size: 0.8rem; color: var(--color-text-muted); }
.recent-chip {
  background: var(--color-surface-2);
  color: var(--color-text);
  border: none;
  border-radius: var(--radius-pill);
  padding: var(--space-1) var(--space-3);
  font-size: 0.85rem;
  font-family: inherit;
  cursor: pointer;
  min-height: 32px;
  transition: background var(--t-fast), transform var(--t-fast);
}
.recent-chip:hover { background: var(--color-border); }
.recent-chip:active { transform: scale(0.96); }

/* ============================================================
 * Invite banner
 * ============================================================ */
.invite-banner {
  width: 100%;
  background: linear-gradient(90deg, var(--color-primary), #38b2ac);
  color: #fff;
  max-height: 280px;
  overflow: hidden;
  box-shadow: var(--shadow-md);
  transition: max-height 0.4s cubic-bezier(0.2, 0.8, 0.3, 1), box-shadow var(--t-base);
}
.invite-banner[data-mode="outgoing"] {
  background: linear-gradient(90deg, var(--color-orange), var(--color-warn));
}
.invite-banner--hidden { max-height: 0; box-shadow: none; }
.invite-banner-inner {
  max-width: 720px;
  margin: 0 auto;
  padding: var(--space-4) var(--space-5);
  display: flex;
  align-items: center;
  gap: var(--space-4);
  flex-wrap: wrap;
}
.invite-banner-text {
  flex: 1 1 auto;
  min-width: 0;
  font-size: 1rem;
  line-height: 1.3;
}
.invite-banner-text strong { font-weight: 700; }
.invite-banner-text .sub {
  display: block;
  font-size: 0.85rem;
  opacity: 0.9;
  margin-top: var(--space-1);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}
.invite-banner[data-mode="outgoing"] .invite-banner-text {
  animation: pulse 1.6s ease-in-out infinite;
}
.invite-banner-actions { display: flex; gap: var(--space-2); flex-shrink: 0; }
.invite-banner-actions button {
  padding: var(--space-2) var(--space-4);
  border: none;
  border-radius: var(--radius-md);
  font-size: 0.9rem;
  font-weight: 600;
  cursor: pointer;
  font-family: inherit;
  min-height: var(--touch-min);
  transition: background var(--t-fast), transform var(--t-fast);
}
.invite-banner-actions button:active { transform: scale(0.96); }
.banner-accept { background: #fff; color: var(--color-text); }
.banner-accept:hover { background: var(--color-surface-2); }
.banner-decline, .banner-withdraw {
  background: rgb(255 255 255 / 0.15);
  color: #fff;
  border: 1px solid rgb(255 255 255 / 0.4);
}
.banner-decline:hover, .banner-withdraw:hover { background: rgb(255 255 255 / 0.25); }
.invite-banner[data-mode="incoming"] .out-actions { display: none; }
.invite-banner[data-mode="outgoing"] .in-actions { display: none; }

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

/* ============================================================
 * Puzzle list
 * ============================================================ */
.puzzle-list {
  display: flex;
  flex-direction: column;
  gap: var(--space-3);
  width: 100%;
  max-width: 420px;
}
.puzzle-link {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  position: relative;
  padding: var(--space-4) var(--space-5);
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  text-decoration: none;
  color: var(--color-text);
  font-size: 1.1rem;
  font-weight: 500;
  box-shadow: var(--shadow-sm);
  transition: box-shadow var(--t-fast), transform var(--t-fast);
}
.puzzle-item:has(.owner-actions) .puzzle-link {
  padding-right: calc(var(--space-3) + 3 * var(--touch-min));
}
.puzzle-link-text { flex: 1; min-width: 0; }
.play-btn {
  flex-shrink: 0;
  padding: var(--space-2) var(--space-4);
  background: var(--color-primary);
  color: #fff;
  border-radius: var(--radius-md);
  font-size: 0.95rem;
  font-weight: 600;
  display: inline-flex;
  align-items: center;
  gap: var(--space-1);
  transition: background var(--t-fast);
}
.puzzle-link:hover .play-btn { background: var(--color-primary-hover); }
.puzzle-link:hover {
  box-shadow: var(--shadow-md);
  transform: translateY(-1px);
  text-decoration: none;
}
.puzzle-link:active { transform: translateY(0); }
.puzzle-link.is-create {
  display: block;
  text-align: center;
  background: var(--color-primary-soft);
  color: var(--color-primary-text);
  margin-bottom: var(--space-3);
}
.check { color: var(--color-success); margin-right: var(--space-2); font-weight: 700; }
.author-line {
  display: block;
  font-size: 0.85rem;
  font-weight: 400;
  color: var(--color-text-muted);
  margin-top: 0.15rem;
}
.created-line {
  display: block;
  font-size: 0.8rem;
  font-weight: 400;
  color: var(--color-text-muted);
  font-style: italic;
}
.puzzle-item { position: relative; }
.puzzle-list:not(.show-duel) .puzzle-item--duel { display: none; }
.puzzle-item.is-pinned .puzzle-link {
  background: #fffbeb;
  border-left: 3px solid #d69e2e;
}
.duel-filter {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  margin-bottom: var(--space-3);
  font-size: 0.9rem;
  color: var(--color-text-muted);
  align-self: flex-start;
  width: 100%;
  max-width: 420px;
  padding-left: var(--space-1);
}
.owner-actions {
  position: absolute;
  top: 50%;
  right: var(--space-2);
  transform: translateY(-50%);
  display: flex;
  gap: 0;
}
.gen-toggle {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  margin: var(--space-2) 0 var(--space-3);
  font-size: 0.9rem;
  color: var(--color-text-muted);
}
.active-duel-text { margin-bottom: var(--space-3); color: var(--color-text-muted); font-size: 0.95rem; }

/* ============================================================
 * Create puzzle
 * ============================================================ */
.form-area {
  width: 100%;
  max-width: 540px;
  display: flex;
  flex-direction: column;
  gap: var(--space-5);
}
.word-sums-list {
  display: flex;
  flex-direction: column;
  gap: var(--space-3);
}
.word-sum-item {
  display: flex;
  flex-direction: column;
  gap: var(--space-1);
}
.word-sum-row {
  display: flex;
  align-items: center;
  gap: var(--space-2);
}
.word-sum-row input {
  flex: 1;
  min-width: 0;
}
.word-sum-row .op {
  font-weight: 600;
  color: var(--color-text-muted);
  font-size: 1.2rem;
  flex-shrink: 0;
}
.word-sum-row .remove-btn {
  background: none;
  border: none;
  color: var(--color-danger);
  font-size: 1.4rem;
  cursor: pointer;
  width: var(--touch-min);
  height: var(--touch-min);
  border-radius: var(--radius-md);
  flex-shrink: 0;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  transition: background var(--t-fast);
}
.word-sum-row .remove-btn:hover { background: var(--color-danger-soft); }
.word-sum-metrics {
  font-size: 0.75rem;
  color: var(--color-text-muted);
  padding-left: var(--space-1);
  font-variant-numeric: tabular-nums;
}
.word-sums-list:not(.show-metrics) .word-sum-metrics { display: none; }

.btn-row {
  display: flex;
  gap: var(--space-3);
  margin-top: var(--space-3);
  flex-wrap: wrap;
}

.gen-panel {
  margin-top: var(--space-4);
  padding: var(--space-4);
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  display: flex;
  flex-direction: column;
  gap: var(--space-3);
}
.gen-panel h3 {
  font-size: 1rem;
  color: var(--color-text);
  margin: 0;
  text-transform: none;
  letter-spacing: normal;
}
.gen-field {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  flex-wrap: wrap;
}
.gen-field label {
  white-space: nowrap;
  flex: 0 0 auto;
  min-width: 140px;
  font-size: 0.9rem;
  margin: 0;
  color: var(--color-text-muted);
}
.gen-field select,
.gen-field input[type="number"] {
  flex: 1;
  min-width: 100px;
}
.gen-field input[type="range"] { flex: 1; min-width: 100px; }
.gen-field .range-value {
  font-variant-numeric: tabular-nums;
  min-width: 2ch;
  text-align: right;
  color: var(--color-text-muted);
  font-size: 0.9rem;
}
.gen-field input[type="checkbox"] { width: 1.1rem; height: 1.1rem; }
.gen-field label[title] { cursor: help; border-bottom: 1px dotted var(--color-text-subtle); }

.advanced-panel {
  border-top: 1px solid var(--color-border);
  padding-top: var(--space-3);
}
.advanced-panel summary {
  cursor: pointer;
  font-size: 0.9rem;
  color: var(--color-text-muted);
  padding: var(--space-1) 0;
  user-select: none;
  list-style: none;
  font-weight: 500;
}
.advanced-panel summary::-webkit-details-marker { display: none; }
.advanced-panel summary::before {
  content: "\25B8";
  display: inline-block;
  margin-right: var(--space-2);
  transition: transform var(--t-fast);
}
.advanced-panel[open] summary::before { transform: rotate(90deg); }
.advanced-fields {
  display: flex;
  flex-direction: column;
  gap: var(--space-3);
  margin-top: var(--space-3);
}

/* ============================================================
 * Puzzle / Duel — board
 * ============================================================ */
.duel-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  margin-bottom: var(--space-4);
  padding: var(--space-2) var(--space-4);
  background: var(--color-primary-soft);
  color: var(--color-primary-text);
  border-radius: var(--radius-pill);
  font-size: 0.9rem;
  font-weight: 600;
  text-decoration: none;
  min-height: 36px;
  transition: background var(--t-fast), transform var(--t-fast);
}
.duel-btn:hover { background: var(--color-primary-soft-2); text-decoration: none; }
.duel-btn:active { transform: scale(0.97); }

.word-bank {
  display: flex;
  flex-wrap: wrap;
  gap: clamp(0.4rem, 1.5vw, 0.6rem);
  justify-content: center;
  max-width: 700px;
  margin-bottom: var(--space-6);
  width: 100%;
}
.word-bubble {
  background: var(--color-primary);
  color: #fff;
  padding: clamp(0.4rem, 1.5vw, 0.55rem) clamp(0.85rem, 3vw, 1.2rem);
  border-radius: var(--radius-pill);
  font-size: clamp(0.9rem, 2.8vw, 1.05rem);
  cursor: grab;
  user-select: none;
  -webkit-user-select: none;
  min-height: 36px;
  display: inline-flex;
  align-items: center;
  transition: transform 0.1s, box-shadow 0.1s, opacity var(--t-fast);
}
.word-bubble:active { cursor: grabbing; }
.word-bubble.dragging { opacity: 0.5; transform: scale(1.05); }
.word-bubble.placed { background: var(--color-text-subtle); cursor: default; }

.equations {
  display: flex;
  flex-direction: column;
  gap: clamp(0.75rem, 2vw, 1.2rem);
  width: 100%;
  max-width: 600px;
}
.equation {
  display: flex;
  align-items: center;
  gap: clamp(0.3rem, 1.2vw, 0.5rem);
  justify-content: center;
  font-weight: 600;
  font-size: clamp(1rem, 3vw, 1.25rem);
}
.drop-box {
  width: clamp(78px, 26vw, 130px);
  height: clamp(42px, 12vw, 48px);
  font-size: clamp(0.85rem, 2.6vw, 1.05rem);
  border: 2px dashed var(--color-border-strong);
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--color-surface);
  font-weight: 500;
  color: var(--color-text);
  user-select: none;
  -webkit-user-select: none;
  transition: border-color var(--t-fast), background var(--t-fast);
}
.drop-box.drag-over { border-color: var(--color-primary); background: var(--color-primary-soft); }
.drop-box.filled {
  border-style: solid;
  border-color: var(--color-primary);
  background: var(--color-primary-soft);
  cursor: grab;
}
.drop-box.filled:active { cursor: grabbing; }
.drop-box.dragging { opacity: 0.5; }
.drop-box.slot-correct  { border-color: var(--color-success); background: var(--color-success-soft); color: var(--color-success-text); }
.drop-box.slot-shuffled,
.drop-box.slot-yellow   { border-color: var(--color-warn);    background: var(--color-warn-soft);    color: var(--color-warn-text);    }
.drop-box.slot-wrong    { border-color: var(--color-danger);  background: var(--color-danger-soft);  color: var(--color-danger-text);  }
.operator { color: var(--color-text-muted); font-size: clamp(1.05rem, 3vw, 1.35rem); }

/* Solved-section collapsible */
.solved-section {
  display: flex;
  flex-direction: column;
  gap: clamp(0.75rem, 2vw, 1.2rem);
}
.solved-section[hidden] { display: none; }
.solved-section:not([hidden]) {
  animation: solved-section-enter 0.35s cubic-bezier(0.2, 0.8, 0.3, 1);
}
@keyframes solved-section-enter {
  from { opacity: 0; transform: translateY(-10px); }
  to   { opacity: 1; transform: translateY(0); }
}
.solved-header {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  background: var(--color-success-soft);
  color: var(--color-success-text);
  border: 2px solid var(--color-success);
  border-radius: var(--radius-pill);
  padding: var(--space-2) var(--space-4);
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  font-family: inherit;
  align-self: center;
  min-height: var(--touch-min);
  transition: background var(--t-fast), box-shadow var(--t-fast), transform var(--t-fast);
}
.solved-header:hover { background: var(--color-success-soft-2); box-shadow: 0 2px 8px rgb(16 185 129 / 0.25); }
.solved-header:active { transform: scale(0.97); }
.solved-chevron {
  display: inline-block;
  font-size: 0.7rem;
  line-height: 1;
  transition: transform 0.3s cubic-bezier(0.2, 0.8, 0.3, 1);
}
.solved-section:not(.collapsed) .solved-chevron { transform: rotate(180deg); }
.solved-list-wrapper {
  display: grid;
  grid-template-rows: 1fr;
  transition: grid-template-rows 0.35s cubic-bezier(0.2, 0.8, 0.3, 1);
}
.solved-section.collapsed .solved-list-wrapper { grid-template-rows: 0fr; }
.solved-list {
  min-height: 0;
  overflow: hidden;
  display: flex;
  flex-direction: column;
  gap: clamp(0.75rem, 2vw, 1.2rem);
}
.solved-list > .equation { animation: solved-row-enter 0.3s cubic-bezier(0.2, 0.8, 0.3, 1); }
@keyframes solved-row-enter {
  from { opacity: 0; transform: translateY(-6px); }
  to   { opacity: 1; transform: translateY(0); }
}

/* ============================================================
 * Duel page layout
 * ============================================================ */
.layout {
  display: grid;
  grid-template-columns: 1fr 280px;
  gap: clamp(1rem, 3vw, 2rem);
  max-width: 1100px;
  margin: 0 auto;
  padding: clamp(1rem, 4vw, 2rem);
  align-items: start;
}
.main {
  display: flex;
  flex-direction: column;
  align-items: center;
  min-width: 0;
}
.main h1 { text-align: center; margin-bottom: var(--space-1); }
.duel-back { align-self: flex-start; margin-bottom: var(--space-2); }
.sidebar {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  padding: var(--space-5);
  box-shadow: var(--shadow-sm);
  position: sticky;
  top: var(--space-5);
}
.sidebar h2 {
  font-size: 0.72rem;
  font-weight: 700;
  color: var(--color-text-muted);
  letter-spacing: 0.08em;
  text-transform: uppercase;
  margin-bottom: var(--space-4);
}
.player {
  display: flex;
  flex-direction: column;
  gap: var(--space-1);
  margin-bottom: var(--space-4);
}
.player:last-of-type { margin-bottom: 0; }
.player-name { font-weight: 600; font-size: 0.95rem; color: var(--color-text); }
.player-name.me { color: var(--color-primary); }
.player-count { font-size: 0.85rem; color: var(--color-text-muted); font-variant-numeric: tabular-nums; }
.bar {
  width: 100%;
  height: 10px;
  background: var(--color-surface-2);
  border-radius: 5px;
  overflow: hidden;
}
.bar-fill {
  height: 100%;
  background: var(--color-primary);
  transition: width 0.4s cubic-bezier(0.2, 0.8, 0.3, 1);
  border-radius: 5px;
}
.player.opponent .bar-fill { background: var(--color-orange); }

.surrender-btn {
  margin-top: var(--space-4);
  width: 100%;
  background: var(--color-danger-soft);
  color: var(--color-danger-text);
  border: 1px solid #fecaca;
  border-radius: var(--radius-md);
  padding: var(--space-2);
  font-size: 0.9rem;
  font-weight: 600;
  cursor: pointer;
  font-family: inherit;
  min-height: var(--touch-min);
  transition: background var(--t-fast), border-color var(--t-fast);
}
.surrender-btn:hover { background: #fecaca; border-color: #fca5a5; }
.surrender-btn:disabled { opacity: 0.55; cursor: default; }

/* ============================================================
 * Result overlays
 * ============================================================ */
.overlay {
  display: none;
  position: fixed;
  inset: 0;
  z-index: 100;
  justify-content: center;
  align-items: center;
  padding: var(--space-5);
  text-align: center;
  animation: overlay-fade-in 0.3s ease;
}
.overlay.show { display: flex; }
@keyframes overlay-fade-in {
  from { opacity: 0; }
  to   { opacity: 1; }
}

.overlay-wrong { background: rgb(220 38 38 / 0.85); }
.overlay-wrong .icon {
  font-size: clamp(8rem, 30vw, 12rem);
  color: #fff;
  animation: shake 0.5s ease;
}
@keyframes shake {
  0%, 100% { transform: translateX(0); }
  20%, 60% { transform: translateX(-15px); }
  40%, 80% { transform: translateX(15px); }
}

.overlay-correct,
.overlay-win,
.overlay-lose {
  flex-direction: column;
  gap: var(--space-4);
}
.overlay-correct { background: rgb(16 185 129 / 0.9); }
.overlay-win     { background: rgb(16 185 129 / 0.92); }
.overlay-lose    { background: rgb(71 85 105 / 0.92); }
.overlay-correct .icon { font-size: clamp(4rem, 14vw, 6rem); color: #fff; }
.overlay-win .icon, .overlay-lose .icon { font-size: clamp(3.5rem, 12vw, 5rem); color: #fff; }
.overlay .message {
  font-size: clamp(1.5rem, 6vw, 2.5rem);
  font-weight: 700;
  color: #fff;
}
.overlay .sub { font-size: 1.05rem; color: #e2e8f0; }

.overlay .back-btn {
  margin-top: var(--space-3);
  padding: var(--space-3) var(--space-6);
  background: #fff;
  color: var(--color-text);
  border: none;
  border-radius: var(--radius-md);
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  text-decoration: none;
  min-height: var(--touch-min);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  transition: transform var(--t-fast);
}
.overlay-correct .back-btn { color: var(--color-success-text); }
.overlay .back-btn:hover { transform: scale(1.05); text-decoration: none; }

.fireworks { position: fixed; inset: 0; pointer-events: none; z-index: 101; }
.spark {
  position: absolute;
  width: 8px; height: 8px;
  border-radius: 50%;
  animation: spark 1s ease-out forwards;
}
@keyframes spark {
  0%   { opacity: 1; transform: translate(0, 0) scale(1); }
  100% { opacity: 0; transform: translate(var(--dx), var(--dy)) scale(0); }
}

/* ============================================================
 * Responsive
 * ============================================================ */
@media (max-width: 900px) {
  .layout {
    grid-template-columns: 1fr;
    gap: var(--space-4);
  }
  .sidebar {
    position: sticky;
    top: 0;
    order: -1;
    padding: var(--space-3) var(--space-4);
  }
  .sidebar h2 { margin-bottom: var(--space-2); }
  .player { margin-bottom: var(--space-2); }
  .surrender-btn { margin-top: var(--space-3); }
}

@media (max-width: 540px) {
  .nav {
    position: static;
    align-self: stretch;
    justify-content: flex-end;
    margin-bottom: var(--space-2);
  }
  .invite-banner-inner { padding: var(--space-3); gap: var(--space-3); }
  .invite-banner-text  { flex: 1 1 100%; }
  .invite-banner-actions { flex: 1 1 100%; }
  .invite-banner-actions button { flex: 1; }
  .gen-field label   { min-width: 100%; flex: 1 1 100%; }
  .gen-field         { gap: var(--space-2); }
  .word-sum-row .op  { font-size: 1rem; }
}