/* ═══════════════════════════════════════════════════════════════
   klickspiele.de – Shared Design System
   Material Design 3 · Orange Accessible · System Fonts Only
   v1.0.0
   ─────────────────────────────────────────────────────────────
   Usage: <link rel="stylesheet" href="./style.css">
   All pages share this file. Game-specific rules are clearly
   marked so subpages that don't have a Sudoku board can safely
   ignore them.
═══════════════════════════════════════════════════════════════ */

/* ══════════════════════════════════════
   1. DESIGN TOKENS
══════════════════════════════════════ */
:root {
  /* Fonts — system stack, no external requests */
  --font-ui:   -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
               "Helvetica Neue", Arial, sans-serif;
  --font-mono: ui-monospace, "Cascadia Mono", "Segoe UI Mono",
               "Roboto Mono", "Courier New", monospace;

  /* Brand colors */
  --c-primary:              #F57C00;
  --c-on-primary:           #FFFFFF;
  --c-primary-container:    #FFE0B2;
  --c-on-primary-container: #2A1400;

  /* Secondary / neutral */
  --c-secondary:              #4A4A4A;
  --c-on-secondary:           #FFFFFF;
  --c-secondary-container:    #EAEAEA;
  --c-on-secondary-container: #111111;

  /* Background & surface */
  --c-bg:          #FFFFFF;
  --c-on-bg:       #111111;
  --c-surface:     #FFFFFF;
  --c-on-surface:  #111111;
  --c-surf-var:    #F2F2F2;
  --c-on-surf-var: #333333;

  /* Surface tones (low → highest) */
  --c-surf-low:     #FAFAFA;
  --c-surf-mid:     #F2F2F2;
  --c-surf-high:    #E8E8E8;
  --c-surf-highest: #DCDCDC;

  /* Outline */
  --c-outline:     #6B6B6B;
  --c-outline-var: #C8C8C8;

  /* Error */
  --c-error:            #B3261E;
  --c-on-error:         #FFFFFF;
  --c-error-container:  #FFDAD6;
  --c-on-error-container: #410002;

  /* Game cell highlights */
  --c-cell-sel:  #FFE0B2;
  --c-cell-rel:  #FFF8F0;
  --c-cell-same: #FFCC80;
  --c-cell-err:  #FFDAD6;

  /* Shape */
  --r-sm:   12px;
  --r-md:   16px;
  --r-lg:   24px;
  --r-xl:   32px;
  --r-full: 9999px;

  /* Motion */
  --dur-fast:   150ms;
  --dur-normal: 220ms;
  --dur-slow:   300ms;
  --ease:       cubic-bezier(0.2, 0, 0, 1);

  /* Elevation */
  --elev-1: 0px 2px 6px rgba(0,0,0,.12);
  --elev-2: 0px 4px 12px rgba(0,0,0,.16);

  /* Layout */
  --touch-min:   56px;
  --btn-h:       64px;
  --content-max: 760px;
  --grid-sz:     min(96vw, 468px);

  /* Accessibility */
  --focus-ring: 3px solid #F57C00;
}

/* ── Reduced-motion support ─────────────────────────────────── */
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: .01ms !important;
    transition-duration: .01ms !important;
  }
}

/* ══════════════════════════════════════
   2. RESET & BASE
══════════════════════════════════════ */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-ui);
  font-size: 18px;
  line-height: 28px;
  background: var(--c-bg);
  color: var(--c-on-bg);
  min-height: 100dvh;
  display: flex;
  flex-direction: column;
  overflow-x: hidden;
}

button { font-family: var(--font-ui); cursor: pointer; border: none; background: none; }
a { color: var(--c-primary); text-decoration: none; }
a:hover { text-decoration: underline; }
img, svg { display: block; max-width: 100%; }

*:focus-visible {
  outline: var(--focus-ring);
  outline-offset: 3px;
  border-radius: 4px;
}

/* ══════════════════════════════════════
   3. RIPPLE EFFECT
══════════════════════════════════════ */
.rpl { position: relative; overflow: hidden; }

.rpl-wave {
  position: absolute;
  border-radius: 50%;
  transform: scale(0);
  background: currentColor;
  opacity: .14;
  pointer-events: none;
  animation: rpl var(--dur-slow) var(--ease) forwards;
}
@keyframes rpl { to { transform: scale(2.8); opacity: 0; } }

/* ══════════════════════════════════════
   4. TOP APP BAR
══════════════════════════════════════ */
.top-bar {
  position: sticky;
  top: 0;
  z-index: 100;
  background: var(--c-primary);
  color: var(--c-on-primary);
  height: 68px;
  padding: 0 8px 0 0;
  display: flex;
  align-items: center;
  gap: 4px;
  box-shadow: var(--elev-1);
}

.top-bar__title {
  flex: 1;
  font-size: 26px;
  font-weight: 600;
  line-height: 34px;
  color: var(--c-on-primary);
  padding-left: 4px;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.top-bar__actions {
  display: flex;
  align-items: center;
  gap: 4px;
  margin-left: auto;
}

/* ── Home button — circle with cursor-pointer icon ────────── */
.home-btn {
  width: 56px;
  height: 56px;
  border-radius: 50%;
  background: rgba(255,255,255,.18);
  border: 2px solid rgba(255,255,255,.35);
  color: var(--c-on-primary);
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  margin: 0 4px;
  text-decoration: none;
  transition: background var(--dur-fast) var(--ease);
  position: relative;
  overflow: hidden;
}
.home-btn:hover         { background: rgba(255,255,255,.28); text-decoration: none; }
.home-btn:active        { background: rgba(255,255,255,.38); }
.home-btn:focus-visible { outline: var(--focus-ring); outline-offset: 2px; }
.home-btn svg { width: 30px; height: 30px; fill: var(--c-on-primary); pointer-events: none; }

/* ── App-bar icon button ─────────────────────────────────── */
.bar-icon-btn {
  width: 56px;
  height: 56px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--c-on-primary);
  transition: background var(--dur-fast) var(--ease);
  position: relative;
  overflow: hidden;
}
.bar-icon-btn::before {
  content: '';
  position: absolute; inset: 0;
  border-radius: 50%;
  background: currentColor;
  opacity: 0;
  transition: opacity var(--dur-fast);
}
.bar-icon-btn:hover::before  { opacity: .10; }
.bar-icon-btn:active::before { opacity: .18; }

/* ── Streak pill ─────────────────────────────────────────── */
.streak-pill {
  display: flex;
  align-items: center;
  gap: 6px;
  height: 36px;
  padding: 0 14px;
  border-radius: var(--r-full);
  background: rgba(255,255,255,.22);
  border: 1.5px solid rgba(255,255,255,.40);
  font-size: 16px;
  font-weight: 600;
  color: var(--c-on-primary);
  white-space: nowrap;
  margin-right: 4px;
}
.streak-pill__fire { font-size: 18px; }

/* ══════════════════════════════════════
   5. SKIP LINK
══════════════════════════════════════ */
.skip {
  position: absolute;
  top: -100%;
  left: 8px;
  z-index: 9999;
  background: var(--c-primary);
  color: var(--c-on-primary);
  padding: 10px 18px;
  border-radius: var(--r-sm);
  font-size: 18px;
  font-weight: 600;
}
.skip:focus { top: 8px; }

/* ══════════════════════════════════════
   6. BUTTONS
══════════════════════════════════════ */

/* Shared state-layer mixin via ::before */
.btn-filled, .btn-tonal, .btn-text, .btn-outlined,
.btn-icon, .fab-chip, .diff-btn, .pill-btn,
.num-btn, .tool-btn {
  -webkit-tap-highlight-color: transparent;
  touch-action: manipulation;
}

/* Filled */
.btn-filled {
  display: inline-flex; align-items: center; justify-content: center; gap: 8px;
  height: var(--btn-h); padding: 0 28px;
  border-radius: var(--r-full);
  background: var(--c-primary); color: var(--c-on-primary);
  font-size: 18px; font-weight: 700;
  box-shadow: var(--elev-1);
  transition: box-shadow var(--dur-fast) var(--ease);
  position: relative; overflow: hidden;
}
.btn-filled::before {
  content: ''; position: absolute; inset: 0; border-radius: inherit;
  background: var(--c-on-primary); opacity: 0; transition: opacity var(--dur-fast);
}
.btn-filled:hover   { box-shadow: var(--elev-2); }
.btn-filled:hover::before  { opacity: .09; }
.btn-filled:active::before { opacity: .15; }

/* Text */
.btn-text {
  display: inline-flex; align-items: center; justify-content: center; gap: 8px;
  height: 52px; padding: 0 20px;
  border-radius: var(--r-full);
  color: var(--c-primary); font-size: 18px; font-weight: 600;
  position: relative; overflow: hidden;
}
.btn-text::before {
  content: ''; position: absolute; inset: 0; border-radius: inherit;
  background: var(--c-primary); opacity: 0; transition: opacity var(--dur-fast);
}
.btn-text:hover::before  { opacity: .07; }
.btn-text:active::before { opacity: .13; }

/* Icon (circle) */
.btn-icon {
  width: var(--touch-min); height: var(--touch-min);
  border-radius: 50%;
  display: flex; align-items: center; justify-content: center;
  color: var(--c-secondary);
  position: relative; overflow: hidden;
}
.btn-icon::before {
  content: ''; position: absolute; inset: 0; border-radius: 50%;
  background: var(--c-primary); opacity: 0; transition: opacity var(--dur-fast);
}
.btn-icon:hover::before  { opacity: .08; }
.btn-icon:active::before { opacity: .14; }
.btn-icon svg { width: 26px; height: 26px; fill: currentColor; pointer-events: none; }

/* ══════════════════════════════════════
   7. COLLAPSIBLE  (details/summary)
══════════════════════════════════════ */
.collapsible {
  background: var(--c-surf-low);
  border-radius: var(--r-lg);
  border: 1.5px solid var(--c-outline-var);
  margin-bottom: 16px;
  overflow: hidden;
}

.collapsible > summary {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 20px 24px;
  font-size: 20px;
  font-weight: 600;
  color: var(--c-on-surface);
  cursor: pointer;
  list-style: none;
  user-select: none;
  gap: 12px;
  transition: background var(--dur-fast) var(--ease);
}
.collapsible > summary::-webkit-details-marker { display: none; }

/* Chevron via CSS mask — no external icon font needed */
.collapsible > summary::after {
  content: '';
  display: block;
  width: 24px;
  height: 24px;
  flex-shrink: 0;
  background-color: var(--c-on-surf-var);
  /* down-chevron SVG, base64-encoded */
  -webkit-mask-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24'%3E%3Cpath d='M7 10l5 5 5-5z'/%3E%3C/svg%3E");
  mask-image:         url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24'%3E%3Cpath d='M7 10l5 5 5-5z'/%3E%3C/svg%3E");
  -webkit-mask-repeat: no-repeat;
  mask-repeat: no-repeat;
  -webkit-mask-position: center;
  mask-position: center;
  transition: transform var(--dur-normal) var(--ease);
}
.collapsible[open] > summary::after {
  transform: rotate(180deg);
}
.collapsible > summary:hover {
  background: var(--c-surf-mid);
}
.collapsible > summary:focus-visible {
  outline: var(--focus-ring);
  outline-offset: -3px;
  border-radius: var(--r-md);
}

.collapsible__body {
  padding: 0 24px 24px;
  border-top: 1.5px solid var(--c-outline-var);
}

/* General text inside collapsible */
.collapsible__body p,
.collapsible__body ul,
.collapsible__body ol {
  font-size: 18px;
  line-height: 28px;
  color: var(--c-on-surf-var);
  margin-top: 16px;
}
.collapsible__body p + p { margin-top: 10px; }
.collapsible__body ul,
.collapsible__body ol   { padding-left: 22px; }
.collapsible__body li   { margin-top: 6px; }
.collapsible__body h3 {
  font-size: 18px;
  font-weight: 600;
  color: var(--c-on-surface);
  margin-top: 20px;
  margin-bottom: 4px;
}

/* ── FAQ items ─────────────────────────────────────────────── */
.faq-item {
  border-top: 1.5px solid var(--c-outline-var);
  padding: 14px 0;
}
.faq-item:first-child { border-top: none; }
.faq-q {
  font-size: 18px;
  font-weight: 600;
  color: var(--c-on-surface);
  margin-bottom: 4px;
}
.faq-a {
  font-size: 17px;
  color: var(--c-on-surf-var);
  line-height: 26px;
}

/* ══════════════════════════════════════
   8. CARDS
══════════════════════════════════════ */
.card {
  background: var(--c-surf-low);
  border-radius: var(--r-lg);
  padding: 24px;
  margin-bottom: 16px;
  border: 1.5px solid var(--c-outline-var);
}
.card h1 {
  font-size: 26px; font-weight: 600; line-height: 34px;
  color: var(--c-on-surface); margin-bottom: 10px;
}
.card h2 {
  font-size: 20px; font-weight: 600; line-height: 30px;
  color: var(--c-on-surface); margin: 18px 0 8px;
}
.card p {
  font-size: 18px; line-height: 28px;
  color: var(--c-on-surf-var); margin-bottom: 10px;
}

/* ── Pill row (quick-links) ─────────────────────────────── */
.pill-row {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin: 12px 0;
}
.pill-btn {
  height: 52px; padding: 0 22px;
  border-radius: var(--r-full);
  background: var(--c-secondary-container);
  color: var(--c-on-secondary-container);
  font-size: 17px; font-weight: 600;
  border: 2px solid var(--c-outline-var);
  cursor: pointer;
  position: relative; overflow: hidden;
  transition: box-shadow var(--dur-fast);
}
.pill-btn::before {
  content: ''; position: absolute; inset: 0; border-radius: inherit;
  background: currentColor; opacity: 0; transition: opacity var(--dur-fast);
}
.pill-btn:hover { box-shadow: var(--elev-1); }
.pill-btn:hover::before  { opacity: .07; }
.pill-btn:active::before { opacity: .13; }

/* ══════════════════════════════════════
   9. DIALOG
══════════════════════════════════════ */
.dialog-scrim {
  position: fixed; inset: 0;
  background: rgba(0,0,0,.40);
  display: flex; align-items: center; justify-content: center;
  z-index: 200; padding: 24px;
  opacity: 0; pointer-events: none;
  transition: opacity var(--dur-slow) var(--ease);
}
.dialog-scrim.show { opacity: 1; pointer-events: all; }
.dialog {
  background: var(--c-surface);
  border-radius: var(--r-xl);
  padding: 28px 24px 24px;
  max-width: 420px; width: 100%;
  box-shadow: var(--elev-2);
  border: 2px solid var(--c-outline-var);
  transform: scale(.93) translateY(14px);
  transition: transform var(--dur-slow) var(--ease);
}
.dialog-scrim.show .dialog { transform: scale(1) translateY(0); }
.dialog-icon  { text-align: center; font-size: 44px; margin-bottom: 14px; }
.dialog-headline {
  font-size: 26px; font-weight: 600; line-height: 34px;
  color: var(--c-on-surface); text-align: center; margin-bottom: 6px;
}
.dialog-body {
  font-size: 18px; line-height: 28px;
  color: var(--c-on-surf-var); text-align: center; margin-bottom: 20px;
}
.dialog-stats {
  display: grid; grid-template-columns: repeat(3,1fr);
  gap: 10px; margin-bottom: 24px;
}
.d-stat {
  background: var(--c-surf-mid);
  border-radius: var(--r-md);
  padding: 14px 8px; text-align: center;
  border: 1.5px solid var(--c-outline-var);
}
.d-stat__lbl {
  font-size: 13px; font-weight: 600;
  letter-spacing: .5px; text-transform: uppercase;
  color: var(--c-on-surf-var); margin-bottom: 4px;
}
.d-stat__val {
  font-family: var(--font-mono);
  font-size: 24px; font-weight: 700;
  color: var(--c-primary);
}
.dialog-actions { display: flex; justify-content: flex-end; gap: 10px; flex-wrap: wrap; }

/* ══════════════════════════════════════
   10. FOOTER
══════════════════════════════════════ */
.site-footer {
  background: var(--c-surf-mid);
  border-top: 2px solid var(--c-outline-var);
  padding: 24px 16px;
  text-align: center;
}
.site-footer__nav {
  display: flex;
  flex-wrap: wrap;
  gap: 6px 20px;
  justify-content: center;
  margin-bottom: 12px;
}
.site-footer__nav a {
  font-size: 16px; font-weight: 600;
  color: var(--c-primary);
}
.site-footer__nav a:hover { text-decoration: underline; }
.site-footer__copy {
  font-size: 15px;
  color: var(--c-on-surf-var);
}

/* ══════════════════════════════════════
   11. GAME-SPECIFIC — LAYOUT
   (only needed on Sudoku pages)
══════════════════════════════════════ */
.game-main { flex: 1; padding-bottom: 195px; }
.game-center {
  display: flex; flex-direction: column;
  align-items: center; padding: 0 8px;
}
.game-left { display: flex; flex-direction: column; align-items: center; }

/* Difficulty row */
.diff-row {
  display: flex; gap: 8px; justify-content: center; flex-wrap: wrap;
  padding: 16px 12px 8px;
  max-width: var(--grid-sz); margin: 0 auto; width: 100%;
}
.diff-btn {
  flex: 1; min-width: 72px; height: var(--btn-h);
  border-radius: var(--r-full);
  font-size: 18px; font-weight: 600;
  color: var(--c-on-surf-var);
  border: 2px solid var(--c-outline);
  background: var(--c-surface);
  display: flex; align-items: center; justify-content: center; gap: 6px;
  transition: all var(--dur-normal) var(--ease);
  position: relative; overflow: hidden;
}
.diff-btn::before {
  content: ''; position: absolute; inset: 0; border-radius: inherit;
  background: currentColor; opacity: 0; transition: opacity var(--dur-fast);
}
.diff-btn:hover::before  { opacity: .07; }
.diff-btn:active::before { opacity: .12; }
.diff-btn.active {
  background: var(--c-primary-container);
  color: var(--c-on-primary-container);
  border-color: var(--c-primary); font-weight: 700;
  box-shadow: var(--elev-1);
}
.diff-btn .tick { display: none; font-style: normal; }
.diff-btn.active .tick { display: inline; }

/* Toolbar */
.toolbar-row {
  display: flex; align-items: center; justify-content: space-between;
  max-width: var(--grid-sz); margin: 0 auto 4px;
  padding: 4px 8px; width: 100%;
}
.toolbar-btns { display: flex; gap: 2px; }
.timer-chip {
  display: flex; align-items: center; gap: 8px;
  height: 48px; padding: 0 18px;
  border-radius: var(--r-full);
  background: var(--c-surf-mid); box-shadow: var(--elev-1);
}
.timer-icon   { font-size: 20px; }
.timer-display {
  font-family: var(--font-mono);
  font-size: 22px; font-weight: 700;
  color: var(--c-on-surface); min-width: 58px;
}
.tool-btn {
  width: var(--touch-min); height: var(--touch-min);
  border-radius: 50%;
  display: flex; align-items: center; justify-content: center;
  color: var(--c-secondary);
  position: relative; overflow: hidden;
}
.tool-btn::before {
  content: ''; position: absolute; inset: 0; border-radius: 50%;
  background: var(--c-primary); opacity: 0; transition: opacity var(--dur-fast);
}
.tool-btn:hover::before  { opacity: .08; }
.tool-btn:active::before { opacity: .14; }
.tool-btn svg { width: 26px; height: 26px; fill: currentColor; pointer-events: none; }

/* FAB row */
.fab-row {
  display: flex; gap: 10px; justify-content: center;
  max-width: var(--grid-sz); margin: 10px auto 0;
  padding: 0 8px; width: 100%;
}
.fab-chip {
  flex: 1; height: var(--btn-h);
  border-radius: var(--r-full);
  background: var(--c-surf-mid); color: var(--c-secondary);
  font-size: 17px; font-weight: 600;
  display: flex; align-items: center; justify-content: center; gap: 8px;
  box-shadow: var(--elev-1); border: 2px solid transparent;
  position: relative; overflow: hidden;
  transition: background var(--dur-normal) var(--ease),
              color     var(--dur-normal) var(--ease),
              box-shadow var(--dur-normal) var(--ease);
}
.fab-chip::before {
  content: ''; position: absolute; inset: 0; border-radius: inherit;
  background: currentColor; opacity: 0; transition: opacity var(--dur-fast);
}
.fab-chip:hover  { box-shadow: var(--elev-2); }
.fab-chip:hover::before  { opacity: .07; }
.fab-chip:active::before { opacity: .13; }
.fab-chip.active {
  background: var(--c-primary-container);
  color: var(--c-on-primary-container);
  border-color: var(--c-primary); box-shadow: var(--elev-2);
}
.fab-chip .fi { font-size: 20px; }

/* Sudoku grid */
#grid-wrap {
  width: var(--grid-sz); margin: 4px auto 0;
  border-radius: var(--r-md); overflow: hidden;
  box-shadow: var(--elev-2); border: 3px solid var(--c-outline);
}
#grid {
  width: 100%; aspect-ratio: 1;
  display: grid; grid-template-rows: repeat(9,1fr);
  background: var(--c-outline-var); gap: 1px;
}
.grid-row { display: grid; grid-template-columns: repeat(9,1fr); gap: 1px; }
.grid-row:nth-child(3) { border-bottom: 2px solid var(--c-outline); }
.grid-row:nth-child(6) { border-bottom: 2px solid var(--c-outline); }

.cell {
  background: var(--c-surface);
  display: flex; align-items: center; justify-content: center;
  cursor: pointer; user-select: none; outline: none;
  position: relative; overflow: hidden; min-height: 44px;
  transition: background var(--dur-fast) var(--ease);
}
.cell:nth-child(3) { border-right: 2px solid var(--c-outline); }
.cell:nth-child(6) { border-right: 2px solid var(--c-outline); }
.cell::after {
  content: ''; position: absolute; inset: 0;
  background: var(--c-primary); opacity: 0;
  transition: opacity var(--dur-fast) var(--ease); pointer-events: none;
}
.cell:hover::after   { opacity: .05; }
.cell:focus-visible  { outline: 2.5px solid var(--c-primary); outline-offset: -2px; z-index: 2; }
.cell.sel  { background: var(--c-cell-sel); }
.cell.rel  { background: var(--c-cell-rel); }
.cell.same { background: var(--c-cell-same); }
.cell.err  { background: var(--c-cell-err); }

.cell-num {
  font-family: var(--font-ui);
  font-size: clamp(15px, 4.5vw, 22px); font-weight: 500; line-height: 1;
  color: var(--c-on-surface); pointer-events: none; z-index: 1;
}
.cell:not(.given) .cell-num { color: var(--c-primary); font-weight: 600; }
.cell.err         .cell-num { color: var(--c-error); }
.cell.given       .cell-num { color: var(--c-on-surface); font-weight: 700; }

.pencil-grid {
  display: none; position: absolute; inset: 1px;
  grid-template-columns: repeat(3,1fr); grid-template-rows: repeat(3,1fr);
  pointer-events: none; z-index: 1;
}
.cell.has-pencil .pencil-grid { display: grid; }
.cell.has-pencil .cell-num    { display: none; }
.pm {
  display: flex; align-items: center; justify-content: center;
  font-size: clamp(7px,1.15vw,10px); font-weight: 600;
  color: var(--c-outline); line-height: 1;
}
.pm.lit { color: var(--c-primary); }

@keyframes num-pop {
  0%   { transform: scale(.55); }
  65%  { transform: scale(1.18); }
  100% { transform: scale(1); }
}
.cell-num.pop { animation: num-pop var(--dur-normal) var(--ease); }

/* Number pad */
.pad-surface {
  position: fixed; bottom: 0; left: 0; right: 0;
  background: var(--c-surf-low);
  border-top: 2px solid var(--c-outline-var);
  border-top-left-radius: var(--r-lg); border-top-right-radius: var(--r-lg);
  box-shadow: 0 -4px 16px rgba(0,0,0,.10);
  padding: 10px 14px calc(12px + env(safe-area-inset-bottom));
  z-index: 50;
}
.pad-handle {
  width: 40px; height: 5px;
  background: var(--c-outline-var);
  border-radius: var(--r-full); margin: 0 auto 10px;
}
.pad-grid {
  display: grid; grid-template-columns: repeat(5,1fr);
  gap: 8px; max-width: 480px; margin: 0 auto;
}
.num-btn {
  height: var(--btn-h); border-radius: var(--r-md);
  background: var(--c-secondary-container); color: var(--c-on-secondary-container);
  font-family: var(--font-mono); font-size: 26px; font-weight: 700;
  display: flex; align-items: center; justify-content: center;
  position: relative; overflow: hidden; border: 2px solid transparent;
  transition: background var(--dur-normal) var(--ease),
              color     var(--dur-normal) var(--ease),
              box-shadow var(--dur-normal) var(--ease),
              border-color var(--dur-normal) var(--ease);
}
.num-btn::before {
  content: ''; position: absolute; inset: 0; border-radius: inherit;
  background: currentColor; opacity: 0; transition: opacity var(--dur-fast);
}
.num-btn:hover::before   { opacity: .07; }
.num-btn:active::before  { opacity: .13; }
.num-btn:hover   { box-shadow: var(--elev-1); }
.num-btn.active  { background: var(--c-primary); color: var(--c-on-primary); box-shadow: var(--elev-2); }
.num-btn.erase-btn {
  font-family: var(--font-ui);
  font-size: 14px; font-weight: 700; letter-spacing: .3px; text-transform: uppercase;
  background: var(--c-surface); color: var(--c-secondary);
  border-color: var(--c-outline-var);
}
.pad-surface.pencil-on .num-btn:not(.erase-btn) {
  background: var(--c-primary-container); color: var(--c-on-primary-container);
  border-color: var(--c-primary);
}
.pad-surface.pencil-on .num-btn.active {
  background: var(--c-primary); color: var(--c-on-primary);
}

/* Confetti canvas */
#cv { position: fixed; inset: 0; pointer-events: none; z-index: 300; display: none; }

/* SEO section wrapper */
.seo-section { max-width: var(--content-max); margin: 32px auto 0; padding: 0 16px 60px; }

/* ══════════════════════════════════════
   12. DARK MODE
   Toggle by adding class "dark-mode" to <body>
══════════════════════════════════════ */
body.dark-mode {
  --c-bg:          #1A1A1A;
  --c-on-bg:       #F0F0F0;
  --c-surface:     #1A1A1A;
  --c-on-surface:  #F0F0F0;
  --c-surf-var:    #2A2A2A;
  --c-on-surf-var: #CCCCCC;
  --c-surf-low:    #232323;
  --c-surf-mid:    #2A2A2A;
  --c-surf-high:   #333333;
  --c-outline-var: #444444;
  --c-secondary-container:    #2D2D2D;
  --c-on-secondary-container: #E0E0E0;
  --c-cell-sel:  #4A2800;
  --c-cell-rel:  #1F1507;
  --c-cell-same: #3D2000;
  --c-cell-err:  #3B0A08;
}

/* ══════════════════════════════════════
   13. DESKTOP ≥ 900px
══════════════════════════════════════ */
@media (min-width: 900px) {
  :root { --grid-sz: 480px; }

  .game-main { padding-bottom: 28px; }
  .game-center {
    flex-direction: row; align-items: flex-start;
    justify-content: center; gap: 32px; padding: 24px 24px 0;
  }
  .game-left { flex-shrink: 0; }

  .pad-surface {
    position: static;
    border-radius: var(--r-lg); box-shadow: var(--elev-1);
    padding: 20px; width: 240px;
    border: 2px solid var(--c-outline-var);
    align-self: flex-start; margin-top: 96px;
  }
  .pad-handle { display: none; }
  .pad-grid { grid-template-columns: repeat(3,1fr); max-width: none; gap: 10px; }
  .num-btn  { height: 68px; font-size: 28px; }
  .fab-row  { justify-content: flex-start; }
}

/* ══════════════════════════════════════
   14. PRINT
══════════════════════════════════════ */
@media print {
  .top-bar, .diff-row, .toolbar-row, .fab-row,
  .pad-surface, .dialog-scrim, .site-footer,
  .seo-section, #cv { display: none !important; }
  .game-main { padding: 0; }
  #grid-wrap {
    box-shadow: none; border: 2px solid #000;
    border-radius: 0; width: 100%; margin: 0;
  }
  :root { --grid-sz: 100%; }
  .cell { background: #fff !important; }
  .cell-num { color: #000 !important; }
}