:root {
  --gap: clamp(8px, 2.2vw, 14px);
  --radius: clamp(6px, 1.6vw, 10px);

  /* Classic 2048's warm tile gradient stays untouched; the chrome leans
     green (Flappy Bird's pipes) so the flying tile pops against it. */
  --bg: #f4f1df;
  --ink: #43402c;
  --ink-soft: #69664d;
  --board-bg: #b4c08e;
  --cell-bg: rgba(255, 255, 240, 0.5);
  --overlay-bg: rgba(244, 241, 223, 0.87);
  --surface: #e6e8c8;
  --accent: #677c3d;
  --accent-dark: #466021;
  --link-color: #466021;
  --pipe: #62954a;
  --pipe-dark: #3f6a2c;

  --tile-2-bg: #eee4da;      --tile-2-fg: #4a4238;
  --tile-4-bg: #ede0c8;      --tile-4-fg: #4a4238;
  --tile-8-bg: #f2b179;      --tile-8-fg: #fff8f0;
  --tile-16-bg: #f59563;     --tile-16-fg: #fff8f0;
  --tile-32-bg: #f67c5f;     --tile-32-fg: #fff8f0;
  --tile-64-bg: #f65e3b;     --tile-64-fg: #fff8f0;
  --tile-128-bg: #edcf72;    --tile-128-fg: #fff8f0;
  --tile-256-bg: #edcc61;    --tile-256-fg: #fff8f0;
  --tile-512-bg: #edc850;    --tile-512-fg: #fff8f0;
  --tile-1024-bg: #edc53f;   --tile-1024-fg: #fff8f0;
  --tile-2048-bg: #edc22e;   --tile-2048-fg: #fff8f0;
  --tile-super-bg: #3c3a32;  --tile-super-fg: #f9f6f2;
}

* { box-sizing: border-box; }

/* Page-level rules (body background, font, scrolling) live in
   assets/site.css — the game only lays out inside .sf-stage, which is sized
   to exactly one screen below the site header. */
.app {
  width: 100%;
  max-width: 560px;
  height: 100%;
  max-height: 820px;
  padding: clamp(4px, 1.5vw, 12px) clamp(12px, 3vw, 24px) clamp(12px, 3vw, 24px);
  color: var(--ink);
  display: flex;
  flex-direction: column;
  gap: clamp(8px, 2.5vw, 16px);
}

.side-panel {
  display: contents;
}

.heading { order: 1; }
.above-game { order: 2; }
.board-wrap { order: 3; }

.heading {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 8px 10px;
}

.title-block {
  display: flex;
  align-items: center;
  gap: 8px;
  flex-shrink: 0;
}

.title {
  margin: 0;
  line-height: 1;
  font-size: clamp(22px, 5.5vw, 30px);
  font-weight: 800;
  color: var(--ink);
  letter-spacing: 0.5px;
}

.title-sub {
  display: inline-block;
  padding: 3px 10px;
  font-size: clamp(10px, 2.8vw, 13px);
  font-weight: 800;
  text-transform: uppercase;
  letter-spacing: 1.5px;
  color: #fff;
  background: var(--accent-dark);
  border-radius: 999px;
}

.scores-container {
  display: flex;
  gap: 8px;
  /* If a long score pushes this onto its own row, keep it right-aligned. */
  margin-left: auto;
}

.score-box {
  background: var(--accent);
  color: #fff;
  border-radius: var(--radius);
  padding: 4px 12px;
  min-width: 58px;
  text-align: center;
  display: flex;
  flex-direction: column;
  line-height: 1.15;
}

.score-label {
  font-size: 10px;
  font-weight: 700;
  text-transform: uppercase;
  opacity: 0.9;
  letter-spacing: 0.5px;
}

.score-value {
  font-size: clamp(14px, 3.2vw, 18px);
  font-weight: 700;
}

.above-game {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 8px 10px;
}

.game-intro {
  margin: 0;
  font-size: clamp(12px, 3vw, 14px);
  color: var(--ink-soft);
  line-height: 1.4;
}

.game-actions {
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  justify-content: flex-end;
  gap: 8px;
  max-width: 100%;
  margin-left: auto;
}

.btn-new-game {
  flex-shrink: 0;
  border: none;
  background: var(--accent-dark);
  color: #fff;
  font-weight: 700;
  font-size: clamp(12px, 3vw, 14px);
  padding: 10px 16px;
  border-radius: var(--radius);
  cursor: pointer;
  touch-action: manipulation;
}

.btn-new-game:active {
  background: var(--accent);
}

.btn-theme-toggle {
  flex-shrink: 0;
  border: none;
  background: var(--surface);
  color: var(--ink);
  line-height: 1;
  width: clamp(34px, 8vw, 40px);
  height: clamp(34px, 8vw, 40px);
  border-radius: var(--radius);
  cursor: pointer;
  touch-action: manipulation;
  display: flex;
  align-items: center;
  justify-content: center;
}

.btn-theme-toggle svg {
  width: 55%;
  height: 55%;
}

.btn-theme-toggle .icon-moon {
  display: none;
}

:root[data-theme="dark"] .btn-theme-toggle .icon-sun {
  display: none;
}

:root[data-theme="dark"] .btn-theme-toggle .icon-moon {
  display: block;
}

.btn-theme-toggle:active {
  background: var(--cell-bg);
}

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

.board {
  position: relative;
  width: min(100%, 500px);
  aspect-ratio: 1 / 1;
  background: var(--board-bg);
  border-radius: calc(var(--radius) + 4px);
  padding: var(--gap);
  overflow: hidden;
  touch-action: none;
  user-select: none;
  -webkit-user-select: none;
  -webkit-touch-callout: none;
}

.grid-bg {
  position: absolute;
  inset: var(--gap);
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  grid-template-rows: repeat(4, 1fr);
  gap: var(--gap);
}

.grid-bg .cell {
  background: var(--cell-bg);
  border-radius: var(--radius);
}

/* Walls and the bird live in a clipped layer so they slide in and out from
   behind the grid edges instead of poking into the board's padding. */
.tile-layer {
  position: absolute;
  inset: var(--gap);
  overflow: hidden;
}

.piece {
  position: absolute;
  left: 0;
  top: 0;
  will-change: transform;
}

.pipe {
  border-radius: var(--radius);
  background: linear-gradient(135deg, var(--pipe) 0%, var(--pipe-dark) 100%);
  box-shadow: inset 0 0 0 3px rgba(255, 255, 255, 0.2), 0 1px 3px rgba(0, 0, 0, 0.25);
}

.bird .face {
  position: relative;
  width: 100%;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius);
  font-weight: 700;
  background: var(--tile-2-bg);
  color: var(--tile-2-fg);
  box-shadow: 0 2px 5px rgba(0, 0, 0, 0.28);
}

/* Progress toward the next merge, drawn on the tile itself so it needs no
   extra layout room. */
.bird .face::before,
.bird .face::after {
  content: "";
  position: absolute;
  left: 14%;
  bottom: 9%;
  height: 5%;
  min-height: 2px;
  border-radius: 999px;
}

.bird .face::before {
  width: 72%;
  background: rgba(0, 0, 0, 0.13);
}

.bird .face::after {
  width: calc(72% * var(--progress, 0));
  background: rgba(0, 0, 0, 0.38);
}

.bird[data-value="2"]    .face { background: var(--tile-2-bg);    color: var(--tile-2-fg); }
.bird[data-value="4"]    .face { background: var(--tile-4-bg);    color: var(--tile-4-fg); }
.bird[data-value="8"]    .face { background: var(--tile-8-bg);    color: var(--tile-8-fg); }
.bird[data-value="16"]   .face { background: var(--tile-16-bg);   color: var(--tile-16-fg); }
.bird[data-value="32"]   .face { background: var(--tile-32-bg);   color: var(--tile-32-fg); }
.bird[data-value="64"]   .face { background: var(--tile-64-bg);   color: var(--tile-64-fg); }
.bird[data-value="128"]  .face { background: var(--tile-128-bg);  color: var(--tile-128-fg); }
.bird[data-value="256"]  .face { background: var(--tile-256-bg);  color: var(--tile-256-fg); }
.bird[data-value="512"]  .face { background: var(--tile-512-bg);  color: var(--tile-512-fg); }
.bird[data-value="1024"] .face { background: var(--tile-1024-bg); color: var(--tile-1024-fg); }
.bird[data-value="2048"] .face { background: var(--tile-2048-bg); color: var(--tile-2048-fg); }
.bird[data-super="true"] .face { background: var(--tile-super-bg); color: var(--tile-super-fg); }

.bird .face.flap {
  animation: flap 140ms ease-out;
}

.bird .face.merged {
  animation: pop 220ms ease-in-out;
}

.bird.crashed .face {
  outline: 3px solid #e74c3c;
  outline-offset: -3px;
  filter: saturate(1.3);
}

.bird.grace .face {
  animation: blink 220ms steps(2, start) infinite;
}

@keyframes flap {
  0%   { transform: scale(1, 1); }
  40%  { transform: scale(1.08, 0.88); }
  100% { transform: scale(1, 1); }
}

@keyframes pop {
  0%   { transform: scale(0.5); }
  60%  { transform: scale(1.18); }
  100% { transform: scale(1); }
}

@keyframes blink {
  0%   { opacity: 1; }
  100% { opacity: 0.45; }
}

@media (prefers-reduced-motion: reduce) {
  .bird .face.flap,
  .bird .face.merged,
  .bird.grace .face { animation: none; }
}

.hint {
  position: absolute;
  left: 50%;
  top: 9%;
  transform: translate(-50%, -50%);
  z-index: 6;
  padding: 0.45em 1em;
  border-radius: 999px;
  background: rgba(35, 40, 20, 0.7);
  color: #fff;
  font-size: var(--hint-size, 14px);
  font-weight: 700;
  white-space: nowrap;
  pointer-events: none;
}

.hint[hidden] { display: none; }

.overlay {
  position: absolute;
  inset: 0;
  background: var(--overlay-bg);
  border-radius: calc(var(--radius) + 4px);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 10;
}

.overlay[hidden] { display: none; }

.overlay-box {
  text-align: center;
  padding: var(--overlay-box-padding, 16px);
  max-width: 100%;
  max-height: 100%;
  overflow: hidden;
}

.overlay-title {
  font-size: var(--overlay-title-size, clamp(22px, 6vw, 32px));
  font-weight: 800;
  margin: 0 0 var(--overlay-title-gap, 16px);
  color: var(--ink);
  line-height: 1.2;
}

.overlay-sub {
  font-size: var(--overlay-sub-size, 14px);
  font-weight: 600;
  margin: calc(var(--overlay-title-gap, 16px) * -0.5) 0 var(--overlay-title-gap, 16px);
  color: var(--ink-soft);
  line-height: 1.2;
}

.overlay-sub[hidden] { display: none; }

.overlay-actions {
  display: flex;
  gap: var(--overlay-actions-gap, 10px);
  justify-content: center;
  flex-wrap: wrap;
}

.btn-overlay {
  border: none;
  border-radius: var(--radius);
  padding: var(--overlay-btn-padding, 10px 18px);
  font-weight: 700;
  font-size: var(--overlay-btn-size, clamp(13px, 3.4vw, 15px));
  cursor: pointer;
  touch-action: manipulation;
}

.btn-primary {
  background: var(--accent-dark);
  color: #fff;
}

.btn-secondary {
  background: var(--surface);
  color: var(--ink);
}

@media (max-height: 700px) {
  .app {
    gap: 4px;
    padding: 8px clamp(12px, 3vw, 24px);
  }
  .game-intro {
    display: none;
  }
  .title {
    font-size: clamp(20px, 6vw, 32px);
  }
  .score-box {
    padding: 3px 10px;
  }
  .btn-new-game {
    padding: 6px 12px;
  }
}

@media (max-height: 300px) {
  .title-sub {
    display: none;
  }
  .app {
    padding: 6px clamp(12px, 3vw, 24px);
    gap: 2px;
  }
  .btn-new-game {
    padding: 2px 10px;
    font-size: 11px;
  }
}

@media (max-width: 260px) {
  .btn-new-game {
    padding: 6px 8px;
    font-size: 11px;
  }
  .btn-theme-toggle {
    width: 26px;
    height: 26px;
    font-size: 12px;
  }
  .game-actions {
    gap: 4px;
  }
}

@media (max-height: 220px) {
  .app {
    padding: 4px clamp(12px, 3vw, 24px);
    gap: 1px;
  }
  .title {
    font-size: 14px;
    letter-spacing: 0;
  }
  .score-box {
    padding: 1px 6px;
    min-width: 36px;
  }
  .score-label {
    font-size: 7px;
  }
  .score-value {
    font-size: 11px;
  }
  .btn-new-game {
    padding: 1px 8px;
    font-size: 10px;
  }
  .btn-theme-toggle {
    width: 20px;
    height: 20px;
    font-size: 11px;
  }
}

:root[data-theme="dark"] {
  --bg: #161a12;
  --ink: #eef0dc;
  --ink-soft: #b6bd96;
  --board-bg: #26301c;
  --cell-bg: rgba(230, 255, 190, 0.07);
  --overlay-bg: rgba(22, 26, 18, 0.87);
  --surface: #2f3a22;
  --accent: #617e38;
  --accent-dark: #46612a;
  --link-color: #b8d583;
  --pipe: #4c7e36;
  --pipe-dark: #2f5222;
}

/* A real-time game on a page that scrolls: no text selection or double-tap zoom
   while tapping around the game area (the article below stays selectable). */
.sf-stage {
  user-select: none;
  -webkit-user-select: none;
  touch-action: manipulation;
  -webkit-tap-highlight-color: transparent;
}