:root {
  --green:   #6aaa64;
  --yellow:  #c9b458;
  --red:     #e53e3e;
  --gray:    #787c7e;
  --bg:      #ffffff;
  --text:    #1a1a1b;
  --border:  #d3d6da;
  --border-filled: #878a8c;
  --header-bg:  #ffffff;
  --modal-bg:   #ffffff;
  --modal-overlay: rgba(0,0,0,0.5);
  --cell-bg:    #ffffff;
  --cell-border: #d3d6da;
  --path-bg:    rgba(106,170,100,0.18);
  --path-color: #6aaa64;
  --key-bg:     #d3d6da;
  --key-text:   #1a1a1b;
}

body.dark {
  --bg:      #121213;
  --text:    #ffffff;
  --border:  #3a3a3c;
  --border-filled: #565758;
  --header-bg:  #121213;
  --modal-bg:   #1a1a1b;
  --cell-bg:    #1a1a1b;
  --cell-border: #3a3a3c;
  --path-bg:    rgba(106,170,100,0.22);
}

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

body {
  background: var(--bg);
  color: var(--text);
  font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
  display: flex;
  flex-direction: column;
  align-items: center;
  min-height: 100dvh;
  overflow-x: hidden;
}

/* ── Accessibility: keyboard focus ──────────────────────────────────────── */
:focus-visible {
  outline: 2px solid var(--green);
  outline-offset: 3px;
  border-radius: 4px;
}
/* Remove outline on mouse/touch interaction */
:focus:not(:focus-visible) { outline: none; }

/* ── Load error ──────────────────────────────────────────────────────────── */
.load-error {
  margin: 60px auto;
  padding: 24px 32px;
  max-width: 320px;
  text-align: center;
  line-height: 1.6;
  border: 1px solid var(--border);
  border-radius: 12px;
  color: var(--gray);
}

/* ── Header ─────────────────────────────────────────────────────────────── */
header {
  width: 100%;
  background: var(--header-bg);
  position: sticky;
  top: 0;
  z-index: 10;
}
.header-inner {
  max-width: 500px;
  margin: 0 auto;
  height: 50px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 12px;
}
header h1 {
  font-size: 1.4rem;
  font-weight: 700;
  letter-spacing: 0.05em;
  text-transform: uppercase;
}
.puzzle-num {
  font-size: 0.6rem;
  font-weight: 400;
  letter-spacing: 0.04em;
  opacity: 0.45;
  margin-left: 7px;
  vertical-align: middle;
  text-transform: none;
}
.header-right { display: flex; gap: 4px; }
.header-border { border-bottom: 1px solid var(--border); }

.icon-btn {
  background: none;
  border: none;
  cursor: pointer;
  color: var(--text);
  padding: 6px;
  border-radius: 6px;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: background 0.15s;
}
.icon-btn:hover { background: var(--border); }
.icon-btn svg { width: 22px; height: 22px; }

/* ── Toast ──────────────────────────────────────────────────────────────── */
#toast-container {
  position: fixed;
  top: 60px;
  left: 50%;
  transform: translateX(-50%);
  z-index: 100;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 8px;
  pointer-events: none;
}
.toast {
  background: var(--text);
  color: var(--bg);
  padding: 10px 16px;
  border-radius: 8px;
  font-size: 0.875rem;
  font-weight: 600;
  animation: toast-in 0.2s ease;
  white-space: nowrap;
}
@keyframes toast-in {
  from { opacity: 0; transform: translateY(-8px); }
  to   { opacity: 1; transform: translateY(0); }
}

/* ── Main layout ────────────────────────────────────────────────────────── */
main {
  flex: 1;
  width: 100%;
  max-width: 500px;
  display: flex;
  flex-direction: column;
  align-items: center;
  padding: 10px 12px 12px;
  gap: 10px;
}

/* ── Target display ─────────────────────────────────────────────────────── */
#target-display {
  font-size: 1rem;
  font-weight: 600;
  opacity: 0.7;
  text-align: center;
  letter-spacing: 0.04em;
  text-transform: uppercase;
}
#target-num {
  font-size: 2.2rem;
  font-weight: 800;
  opacity: 1;
  color: var(--text);
  display: block;
  line-height: 1;
}

/* ── Grid ───────────────────────────────────────────────────────────────── */
#grid-container {
  position: relative;
  width: min(calc(100vw - 24px), 340px);
  height: min(calc(100vw - 24px), 340px);
  touch-action: none;
  user-select: none;
  -webkit-user-select: none;
}
#game-grid {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  grid-template-rows: repeat(5, 1fr);
  gap: 4px;
  width: 100%;
  height: 100%;
}

.cell {
  background: var(--cell-bg);
  border: 2px solid var(--cell-border);
  border-radius: 8px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  cursor: pointer;
  position: relative;
  transition: background 0.12s, border-color 0.12s;
  -webkit-tap-highlight-color: transparent;
  overflow: hidden;
}
.cell-val {
  font-size: min(7vw, 1.6rem);
  line-height: 1;
  pointer-events: none;
}
.cell-seq {
  position: absolute;
  top: 2px;
  right: 4px;
  font-size: min(2.5vw, 0.55rem);
  font-weight: 600;
  opacity: 0.75;
  pointer-events: none;
  line-height: 1;
}

/* Path states */
.cell.in-path {
  background: var(--path-bg);
  border-color: var(--path-color);
}
.cell.path-start {
  background: var(--green);
  border-color: var(--green);
  color: #fff;
}
.cell.path-end {
  background: rgba(106,170,100,0.35);
  border-color: var(--green);
}
.cell.sum-ok {
  animation: pulse-green 0.35s ease;
}
.cell.sum-exceeded {
  background: rgba(229, 62, 62, 0.15) !important;
  border-color: var(--red) !important;
}
.cell.sum-exceeded.path-start {
  background: rgba(229, 62, 62, 0.50) !important;
  color: #fff !important;
}
.cell.sum-over {
  animation: flash-red 0.3s ease;
  border-color: var(--red) !important;
}
.cell.solved {
  background: rgba(201,180,88,0.25);
  border-color: var(--yellow);
}
.cell.solved.path-start {
  background: var(--yellow);
  border-color: var(--yellow);
  color: #fff;
}
.cell.three-star {
  background: rgba(106,170,100,0.28);
  border-color: var(--green);
}
.cell.three-star.path-start {
  background: var(--green);
  border-color: var(--green);
  color: #fff;
}
.cell.optimal-path {
  background: rgba(99,148,222,0.22);
  border-color: #6394de;
  animation: pop-in 0.2s ease;
}
.cell.optimal-path.path-start {
  background: #6394de;
  border-color: #6394de;
  color: #fff;
}

@keyframes pop-in {
  0%   { transform: scale(0.88); }
  60%  { transform: scale(1.06); }
  100% { transform: scale(1); }
}

@keyframes pulse-green {
  0%   { transform: scale(1); border-color: var(--green); }
  50%  { transform: scale(1.06); border-color: var(--green); box-shadow: 0 0 0 3px rgba(106,170,100,0.3); }
  100% { transform: scale(1); }
}
@keyframes flash-red {
  0%,100% { border-color: var(--red); }
  50%     { background: rgba(229,62,62,0.15); border-color: var(--red); }
}

/* ── SVG path overlay ───────────────────────────────────────────────────── */
#path-svg {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  pointer-events: none;
  overflow: visible;
}
#path-line {
  fill: none;
  stroke: rgba(106,170,100,0.65);
  stroke-linecap: round;
  stroke-linejoin: round;
  transition: stroke 0.2s;
}

/* ── Info bar ───────────────────────────────────────────────────────────── */
#info-bar {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0;
  width: 100%;
  max-width: 340px;
}
.info-col {
  flex: 1;
  text-align: center;
}
.info-label {
  font-size: 0.65rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  opacity: 0.6;
  margin-bottom: 2px;
}
.info-val {
  font-size: 1.6rem;
  font-weight: 700;
  line-height: 1;
  transition: color 0.25s;
}
.info-val.sum-match { color: var(--green); }
.info-val.sum-over  { color: var(--red);   }
.info-divider {
  width: 1px;
  height: 32px;
  background: var(--border);
  margin: 0 8px;
}

/* ── Action bar ─────────────────────────────────────────────────────────── */
#action-bar {
  display: flex;
  gap: 10px;
  width: 100%;
  max-width: 340px;
}
.btn-secondary {
  flex: 1;
  background: none;
  border: 2px solid var(--border-filled);
  color: var(--text);
  padding: 12px 0;
  border-radius: 10px;
  font-size: 0.9rem;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.15s;
  -webkit-tap-highlight-color: transparent;
}
.btn-secondary:hover { background: var(--border); }
.btn-primary {
  flex: 1.5;
  background: var(--text);
  color: var(--bg);
  border: none;
  padding: 12px 0;
  border-radius: 10px;
  font-size: 0.9rem;
  font-weight: 700;
  cursor: pointer;
  letter-spacing: 0.03em;
  transition: opacity 0.15s;
  -webkit-tap-highlight-color: transparent;
}
.btn-primary:hover:not(:disabled) { opacity: 0.85; }
.btn-primary:disabled {
  opacity: 0.3;
  cursor: not-allowed;
}

/* ── Result panel ───────────────────────────────────────────────────────── */
#result-panel {
  width: 100%;
  max-width: 340px;
  text-align: center;
  padding: 16px;
  border: 1px solid var(--border);
  border-radius: 12px;
  animation: toast-in 0.3s ease;
}
.result-stars  { font-size: 1.8rem; margin-bottom: 6px; }
.result-title  { font-size: 1.15rem; font-weight: 700; margin-bottom: 4px; }
.result-sub    { font-size: 0.82rem; opacity: 0.7; margin-bottom: 6px; }
.result-meta   { font-size: 0.8rem; opacity: 0.6; margin-bottom: 12px; }
.result-actions {
  display: flex;
  flex-direction: column;
  gap: 8px;
  align-items: stretch;
}
.result-actions .btn-primary,
.result-actions .btn-secondary {
  width: 100%;
  padding: 11px 16px;
  box-sizing: border-box;
}
.result-retry-blocked {
  margin-top: 10px;
  font-size: 0.75rem;
  opacity: 0.5;
  font-style: italic;
}

/* ── Modals ─────────────────────────────────────────────────────────────── */
.modal-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: var(--modal-overlay);
  z-index: 50;
  align-items: center;
  justify-content: center;
  padding: 16px;
}
.modal-overlay.open { display: flex; }
.modal {
  background: var(--modal-bg);
  border-radius: 12px;
  width: 100%;
  max-width: 420px;
  max-height: 85dvh;
  overflow-y: auto;
  box-shadow: 0 4px 32px rgba(0,0,0,0.3);
  animation: modal-in 0.2s ease;
}
@keyframes modal-in {
  from { opacity: 0; transform: scale(0.96) translateY(8px); }
  to   { opacity: 1; transform: scale(1) translateY(0); }
}
.modal-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 16px 20px 12px;
  border-bottom: 1px solid var(--border);
}
.modal-header h2 {
  font-size: 1rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
}
.modal-close {
  background: none;
  border: none;
  font-size: 1.1rem;
  cursor: pointer;
  color: var(--text);
  padding: 4px 6px;
  border-radius: 4px;
  opacity: 0.7;
  transition: opacity 0.15s;
}
.modal-close:hover { opacity: 1; }
.modal-body {
  padding: 16px 20px 20px;
  display: flex;
  flex-direction: column;
  gap: 12px;
  font-size: 0.9rem;
  line-height: 1.5;
}
.modal-body h3 {
  font-size: 0.85rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  margin-top: 4px;
}
.modal-body a { color: var(--green); }

/* How-to-play examples */
.htp-grid-demo {
  display: grid;
  grid-template-columns: repeat(5, 36px);
  grid-template-rows: repeat(5, 36px);
  gap: 3px;
  position: relative;
  margin: 4px auto;
}
.htp-cell {
  width: 36px; height: 36px;
  border: 2px solid var(--border);
  border-radius: 6px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 0.95rem;
}
.htp-cell.on {
  background: rgba(106,170,100,0.25);
  border-color: var(--green);
}
.htp-cell.start {
  background: var(--green);
  border-color: var(--green);
  color: #fff;
}
.htp-warning {
  background: rgba(201,180,88,0.15);
  border: 1px solid var(--yellow);
  border-radius: 8px;
  padding: 10px 12px;
  font-size: 0.85rem;
}

/* ── Stats ──────────────────────────────────────────────────────────────── */
#stats-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 8px;
  text-align: center;
}
.stat-block .stat-val {
  font-size: 2rem;
  font-weight: 700;
  line-height: 1;
}
.stat-block .stat-label {
  font-size: 0.65rem;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  opacity: 0.7;
  margin-top: 3px;
}
#result-dist { display: flex; flex-direction: column; gap: 6px; }
.dist-row { display: flex; align-items: center; gap: 8px; font-size: 0.82rem; }
.dist-label { width: 52px; text-align: right; font-weight: 600; opacity: 0.85; }
.dist-bar-wrap { flex: 1; }
.dist-bar {
  min-width: 28px;
  height: 22px;
  border-radius: 4px;
  display: flex;
  align-items: center;
  justify-content: flex-end;
  padding-right: 6px;
  font-size: 0.78rem;
  font-weight: 700;
  color: #fff;
  transition: width 0.4s ease;
}
.bar-three { background: var(--green); }
.bar-two   { background: var(--yellow); }
.bar-one   { background: var(--gray); }

#stats-footer {
  border-top: 1px solid var(--border);
  padding-top: 14px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}
.next-label { font-size: 0.7rem; text-transform: uppercase; opacity: 0.7; letter-spacing: 0.05em; }
#countdown { font-size: 1.4rem; font-weight: 700; font-variant-numeric: tabular-nums; }
#stats-footer .btn-primary { flex: none; padding: 10px 20px; }

/* ── Settings ───────────────────────────────────────────────────────────── */
.setting-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding: 4px 0;
}
.setting-title { font-weight: 600; font-size: 0.95rem; }
.setting-desc  { font-size: 0.78rem; opacity: 0.65; margin-top: 2px; }
.setting-divider { border-top: 1px solid var(--border); margin: 4px 0; }
.setting-link-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding: 4px 0;
}
.setting-links { display: flex; gap: 8px; }
.setting-link {
  background: none;
  border: none;
  color: var(--green);
  font-size: 0.9rem;
  font-weight: 600;
  cursor: pointer;
  padding: 0;
  text-decoration: none;
}
.setting-link:hover { text-decoration: underline; }

.toggle { position: relative; display: inline-block; width: 44px; height: 24px; cursor: pointer; }
.toggle input { position: absolute; opacity: 0; width: 100%; height: 100%; margin: 0; cursor: pointer; }
.toggle-slider {
  position: absolute;
  inset: 0;
  background: var(--border-filled);
  border-radius: 24px;
  transition: background 0.2s;
}
.toggle-slider::before {
  content: '';
  position: absolute;
  width: 18px; height: 18px;
  left: 3px; top: 3px;
  background: #fff;
  border-radius: 50%;
  transition: transform 0.2s;
}
.toggle input:checked + .toggle-slider { background: var(--green); }
.toggle input:checked + .toggle-slider::before { transform: translateX(20px); }

.hidden { display: none !important; }

/* ── Responsive ─────────────────────────────────────────────────────────── */
@media (max-height: 680px) {
  #target-display { font-size: 0.85rem; }
  #target-num     { font-size: 1.8rem; }
  main            { gap: 7px; padding: 7px 12px 8px; }
}
@media (max-height: 580px) {
  main { gap: 5px; padding: 5px 12px 6px; }
  #target-display { display: none; }
}