/* ============================================================
   2048 — warm palette, senior-friendly, iPad-first
   ============================================================ */

:root {
  --bg: #faf7f2;
  --card: #ffffff;
  --text: #3d3229;
  --text-light: #8a7d72;
  --accent: #c9956b;
  --accent-dark: #a6774e;
  --accent-light: #f5e6d3;
  --border: #d4c8bb;
  --border-thick: #8a7d72;
  --board-bg: #b8a389;
  --cell-bg: rgba(238, 228, 218, 0.35);
  --btn-bg: #f0e8de;
  --shadow: 0 4px 20px rgba(90, 70, 50, 0.10);
  --shadow-btn: 0 2px 8px rgba(90, 70, 50, 0.12);
  --radius: 18px;

  /* tile colors (warm gradient) */
  --t2:    #eee4da;
  --t4:    #ede0c8;
  --t8:    #f2b179;
  --t16:   #f59563;
  --t32:   #f67c5f;
  --t64:   #f65e3b;
  --t128:  #edcf72;
  --t256:  #edcc61;
  --t512:  #edc850;
  --t1024: #edc53f;
  --t2048: #edc22e;
  --thigh: #3c3a32;

  /* sizing tokens */
  --title-font: 32px;
  --stat-label-font: 14px;
  --stat-value-font: 30px;
  --tile-font-2: 38px;
  --tile-font-3: 32px;
  --tile-font-4: 24px;
  --dpad-size: 72px;
  --dpad-font: 32px;
  --text-btn-font: 18px;
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  -webkit-tap-highlight-color: transparent;
  -webkit-touch-callout: none;
  user-select: none;
}

html, body {
  height: 100%;
  height: 100dvh;
  overflow: hidden;
}

body {
  font-family: -apple-system, 'PingFang TC', 'Noto Sans TC', 'Helvetica Neue', sans-serif;
  background: var(--bg);
  color: var(--text);
}

.app {
  width: 100%;
  height: 100%;
  height: 100dvh;
  max-width: 900px;
  margin: 0 auto;
  padding: 14px 16px;
  padding-top: calc(14px + env(safe-area-inset-top, 0px));
  padding-bottom: calc(12px + env(safe-area-inset-bottom, 0px));
  display: flex;
  flex-direction: column;
  gap: 12px;
}

/* --- Header --- */

.header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-shrink: 0;
}

.title {
  font-size: var(--title-font);
  font-weight: 800;
  color: var(--accent-dark);
  letter-spacing: 6px;
}

.help-btn, .back-btn {
  width: 48px;
  height: 48px;
  border-radius: 50%;
  border: 2px solid var(--border);
  background: var(--card);
  color: var(--text-light);
  font-size: 22px;
  font-weight: 700;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  text-decoration: none;
  transition: all 0.2s;
  flex-shrink: 0;
}
.help-btn:active, .back-btn:active {
  background: var(--accent-light);
  border-color: var(--accent);
  color: var(--accent);
}

/* --- Status bar --- */

.status-bar {
  display: flex;
  align-items: center;
  justify-content: space-around;
  gap: 10px;
  background: var(--card);
  border: 2px solid var(--border);
  border-radius: var(--radius);
  padding: 10px 14px;
  box-shadow: var(--shadow);
  flex-shrink: 0;
}

.stat {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 2px;
  min-width: 72px;
}

.stat-label {
  font-size: var(--stat-label-font);
  color: var(--text-light);
  letter-spacing: 2px;
  font-weight: 600;
}

.stat-value {
  font-size: var(--stat-value-font);
  font-weight: 800;
  color: var(--text);
  line-height: 1;
}

.stat-value.accent { color: var(--accent-dark); }

.stat-btn {
  border: 2px dashed var(--border);
  background: var(--accent-light);
  border-radius: 14px;
  padding: 6px 14px;
  cursor: pointer;
  transition: transform 0.15s, background 0.15s;
  font-family: inherit;
  color: inherit;
}
.stat-btn:active {
  transform: scale(0.96);
  background: var(--border);
}

/* --- Play area --- */

.play-area {
  flex: 1 1 0;
  display: flex;
  flex-direction: column;
  gap: 14px;
  min-height: 0;
  align-items: center;
  width: 100%;
}

.board-wrap {
  flex: 1 1 0;
  min-height: 0;
  min-width: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  width: 100%;
}

.board {
  position: relative;
  /* size set by JS fitBoard() */
  width: 0;
  height: 0;
  background: var(--board-bg);
  border-radius: var(--radius);
  box-shadow: var(--shadow), inset 0 2px 6px rgba(0,0,0,0.15);
  box-sizing: border-box;
  touch-action: none;
  overflow: hidden;
}

/* --- Cells (empty grid backdrop) --- */
/* 4 tiles + 5 gaps = 100%. gap 2%, tile 22.5%, step 24.5% */
.cell {
  position: absolute;
  width: 22.5%;
  height: 22.5%;
  border-radius: 10px;
  background: var(--cell-bg);
}

/* --- Tiles (absolute positioned over cells) --- */
.tile {
  position: absolute;
  width: 22.5%;
  height: 22.5%;
  border-radius: 10px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 800;
  color: var(--text);
  box-shadow: 0 2px 5px rgba(0,0,0,0.10);
  transition: left 0.13s ease-out, top 0.13s ease-out;
  z-index: 2;
  font-size: var(--tile-font-2);
}

/* Tile colors by value */
.tile[data-value="2"]    { background: var(--t2);   color: #6b5a4a; }
.tile[data-value="4"]    { background: var(--t4);   color: #6b5a4a; }
.tile[data-value="8"]    { background: var(--t8);   color: #fff; }
.tile[data-value="16"]   { background: var(--t16);  color: #fff; }
.tile[data-value="32"]   { background: var(--t32);  color: #fff; }
.tile[data-value="64"]   { background: var(--t64);  color: #fff; }
.tile[data-value="128"]  { background: var(--t128); color: #fff; font-size: var(--tile-font-3); }
.tile[data-value="256"]  { background: var(--t256); color: #fff; font-size: var(--tile-font-3); }
.tile[data-value="512"]  { background: var(--t512); color: #fff; font-size: var(--tile-font-3); }
.tile[data-value="1024"] { background: var(--t1024); color: #fff; font-size: var(--tile-font-4); }
.tile[data-value="2048"] { background: var(--t2048); color: #fff; font-size: var(--tile-font-4);
  box-shadow: 0 0 22px rgba(237, 194, 46, 0.8), 0 2px 5px rgba(0,0,0,0.10); }
.tile[data-value="4096"],
.tile[data-value="8192"],
.tile[data-value="16384"],
.tile[data-value="32768"] { background: var(--thigh); color: #fff; font-size: var(--tile-font-4); }

.tile.new {
  animation: tile-appear 0.18s ease-out;
}
.tile.merged {
  animation: tile-bump 0.18s ease-out;
}

@keyframes tile-appear {
  0%   { transform: scale(0.2); opacity: 0; }
  100% { transform: scale(1);   opacity: 1; }
}
@keyframes tile-bump {
  0%   { transform: scale(1);    }
  50%  { transform: scale(1.15); }
  100% { transform: scale(1);    }
}

/* --- D-pad controls --- */

.controls {
  width: 100%;
  display: flex;
  flex-direction: column;
  gap: 12px;
  align-items: center;
  flex-shrink: 0;
}

.dpad {
  display: flex;
  flex-direction: column;
  gap: 10px;
  align-items: center;
}

.dpad-row {
  display: flex;
  gap: 10px;
  align-items: center;
}

.dpad-spacer {
  width: var(--dpad-size);
  height: var(--dpad-size);
}

.dpad-btn {
  width: var(--dpad-size);
  height: var(--dpad-size);
  border: none;
  border-radius: 18px;
  background: var(--card);
  color: var(--accent-dark);
  font-size: var(--dpad-font);
  font-weight: 700;
  cursor: pointer;
  box-shadow: var(--shadow-btn);
  display: flex;
  align-items: center;
  justify-content: center;
  transition: transform 0.1s, background 0.15s;
}
.dpad-btn:active {
  transform: scale(0.92);
  background: var(--accent-light);
}
.dpad-btn.center {
  background: var(--accent-light);
  color: var(--accent-dark);
  font-size: calc(var(--dpad-font) - 4px);
}
.dpad-btn.center:disabled {
  opacity: 0.35;
  cursor: default;
}

/* --- Text buttons --- */

.text-btn {
  padding: 12px 28px;
  border: 2px solid var(--border);
  border-radius: 16px;
  background: var(--card);
  color: var(--text);
  font-size: var(--text-btn-font);
  font-weight: 700;
  cursor: pointer;
  letter-spacing: 2px;
  transition: all 0.15s;
  box-shadow: var(--shadow-btn);
  font-family: inherit;
}
.text-btn:active {
  transform: scale(0.96);
  background: var(--btn-bg);
}
.text-btn.primary {
  background: var(--accent);
  color: white;
  border-color: var(--accent);
}
.text-btn.primary:active {
  background: var(--accent-dark);
}

/* --- Modal --- */

.modal-overlay {
  position: fixed;
  inset: 0;
  background: rgba(43, 37, 32, 0.5);
  backdrop-filter: blur(6px);
  display: flex;
  align-items: center;
  justify-content: center;
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.3s;
  z-index: 100;
}

.modal-overlay.show {
  opacity: 1;
  pointer-events: all;
}

.modal {
  background: var(--card);
  border-radius: 28px;
  padding: 36px;
  text-align: center;
  max-width: 480px;
  width: 88%;
  box-shadow: 0 10px 40px rgba(0, 0, 0, 0.15);
  border: 3px solid var(--border);
}

.modal h2 {
  font-size: 30px;
  margin-bottom: 12px;
  color: var(--text);
}

.end-sub {
  color: var(--text-light);
  font-size: 18px;
  margin-bottom: 20px;
}

.end-stats {
  display: flex;
  justify-content: center;
  gap: 36px;
  margin-bottom: 24px;
}

.end-stat .label {
  font-size: 14px;
  color: var(--text-light);
  margin-bottom: 4px;
  letter-spacing: 1px;
}
.end-stat .value {
  font-size: 34px;
  font-weight: 800;
  color: var(--accent);
}

.end-actions {
  display: flex;
  gap: 12px;
  justify-content: center;
}

/* Target picker options */
.target-options {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
  margin-bottom: 18px;
}
.target-option {
  padding: 18px 12px;
  border: 3px solid var(--border);
  border-radius: 18px;
  background: var(--card);
  color: var(--text);
  font-family: inherit;
  cursor: pointer;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 4px;
  transition: all 0.15s;
  box-shadow: var(--shadow-btn);
}
.target-option:active { transform: scale(0.96); background: var(--accent-light); }
.target-option.current {
  border-color: var(--accent);
  background: var(--accent-light);
  box-shadow: 0 0 0 3px rgba(201, 149, 107, 0.25), var(--shadow-btn);
}
.target-option .opt-label {
  font-size: 16px;
  color: var(--text-light);
  letter-spacing: 4px;
  font-weight: 600;
}
.target-option .opt-value {
  font-size: 32px;
  color: var(--accent-dark);
  font-weight: 800;
  line-height: 1;
}

.help-content {
  text-align: left;
  max-height: 60vh;
  overflow-y: auto;
  -webkit-overflow-scrolling: touch;
  margin-bottom: 20px;
}

.help-content h3 {
  font-size: 21px;
  margin: 18px 0 10px;
  color: var(--accent);
}
.help-content h3:first-child { margin-top: 0; }

.help-content p,
.help-content li {
  font-size: 18px;
  line-height: 1.7;
  color: var(--text);
}

.help-content ul {
  padding-left: 22px;
  margin-bottom: 14px;
}

/* =============================================================
   TABLET — side-by-side layout for both orientations
   ============================================================= */

@media (min-width: 700px) {
  :root {
    --title-font: 48px;
    --stat-label-font: 20px;
    --stat-value-font: 42px;
    --tile-font-2: 64px;
    --tile-font-3: 54px;
    --tile-font-4: 42px;
    --dpad-size: 96px;
    --dpad-font: 44px;
    --text-btn-font: 22px;
  }

  .app {
    max-width: none;
    padding: 14px 20px;
    padding-top: calc(14px + env(safe-area-inset-top, 0px));
    padding-bottom: calc(14px + env(safe-area-inset-bottom, 0px));
    padding-left: calc(20px + env(safe-area-inset-left, 0px));
    padding-right: calc(20px + env(safe-area-inset-right, 0px));
    gap: 14px;
  }

  .title { letter-spacing: 12px; }
  .help-btn, .back-btn { width: 60px; height: 60px; font-size: 28px; }

  .status-bar { padding: 14px 22px; }
  .stat { min-width: 110px; }

  .play-area {
    flex-direction: row;
    align-items: stretch;
    justify-content: center;
    gap: 28px;
  }

  .controls {
    width: auto;
    min-width: 340px;
    max-width: 440px;
    align-self: center;
    justify-content: center;
    gap: 20px;
  }

  .text-btn { padding: 16px 40px; border-radius: 18px; }

  .target-option { padding: 22px 14px; }
  .target-option .opt-label { font-size: 22px; letter-spacing: 6px; }
  .target-option .opt-value { font-size: 44px; }
  .target-options { gap: 16px; margin-bottom: 22px; }
}

/* Large tablets */
@media (min-width: 1024px) {
  :root {
    --title-font: 58px;
    --stat-value-font: 52px;
    --tile-font-2: 80px;
    --tile-font-3: 66px;
    --tile-font-4: 52px;
    --dpad-size: 118px;
    --dpad-font: 54px;
  }
  .controls { min-width: 420px; max-width: 520px; }
}

/* Small phones */
@media (max-width: 380px) {
  :root {
    --title-font: 22px;
    --stat-label-font: 11px;
    --stat-value-font: 22px;
    --tile-font-2: 24px;
    --tile-font-3: 20px;
    --tile-font-4: 16px;
    --dpad-size: 56px;
    --dpad-font: 22px;
    --text-btn-font: 14px;
  }
  .app { padding: 10px 12px; gap: 8px; }
  .title { letter-spacing: 3px; }
  .stat { min-width: 56px; }
}