:root {
  color-scheme: dark;
  font-family: Inter, ui-rounded, "SF Pro Rounded", "PingFang SC", "Microsoft YaHei", system-ui, sans-serif;
  background: #070b16;
  color: #f4f7ff;
  font-synthesis: none;
  --ink: #f4f7ff;
  --muted: #8e98ad;
  --panel: rgba(16, 23, 42, 0.88);
  --line: rgba(255, 255, 255, 0.09);
  --cyan: #6fffe9;
  --violet: #8f7cff;
  --cell: rgba(255, 255, 255, 0.055);
  --gap: clamp(0.5rem, 2.2vw, 0.75rem);
}

* { box-sizing: border-box; }

html {
  min-height: 100%;
  background: #070b16;
  overscroll-behavior: none;
}

body {
  min-width: 320px;
  min-height: 100svh;
  margin: 0;
  overflow-x: hidden;
  background:
    radial-gradient(circle at 20% 0%, rgba(79, 62, 170, 0.35), transparent 34rem),
    radial-gradient(circle at 100% 75%, rgba(20, 172, 158, 0.18), transparent 30rem),
    #070b16;
}

button { font: inherit; }
[hidden] { display: none !important; }

.app-shell {
  width: min(100%, 34rem);
  min-height: 100svh;
  margin: 0 auto;
  padding: max(1.25rem, env(safe-area-inset-top)) 1.1rem max(1rem, env(safe-area-inset-bottom));
  display: flex;
  flex-direction: column;
  justify-content: center;
  gap: clamp(1.15rem, 3.5vh, 2rem);
}

.topbar {
  display: flex;
  align-items: flex-end;
  justify-content: space-between;
  gap: 1rem;
}

.eyebrow {
  margin: 0 0 0.1rem;
  color: var(--cyan);
  font-size: 0.72rem;
  font-weight: 800;
  letter-spacing: 0.18em;
}

h1 {
  margin: 0;
  font-size: clamp(3.25rem, 18vw, 5.8rem);
  line-height: 0.78;
  letter-spacing: -0.07em;
  font-weight: 900;
}

.scoreboard {
  display: flex;
  gap: 0.5rem;
}

.score-card {
  position: relative;
  min-width: 4.4rem;
  padding: 0.55rem 0.65rem 0.6rem;
  border: 1px solid var(--line);
  border-radius: 0.9rem;
  background: rgba(255, 255, 255, 0.045);
  text-align: center;
  backdrop-filter: blur(12px);
}

.score-card span {
  display: block;
  color: var(--muted);
  font-size: 0.72rem;
  font-weight: 700;
}

.score-card strong {
  display: block;
  margin-top: 0.1rem;
  font-size: 1.1rem;
  line-height: 1.1;
}

.account-bar {
  margin-top: -0.35rem;
  padding: 0.7rem 0.8rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.75rem;
  border: 1px solid var(--line);
  border-radius: 1rem;
  background: rgba(255, 255, 255, 0.035);
}

.account-bar strong,
.account-bar small { display: block; }
.account-bar strong { font-size: 0.88rem; }
.account-bar small { margin-top: 0.12rem; color: var(--muted); font-size: 0.72rem; }
.account-actions { display: flex; align-items: center; gap: 0.35rem; }
.compact-action { min-height: 2.25rem; padding: 0 0.75rem; font-size: 0.8rem; }
.text-action { min-height: 2.25rem; padding: 0 0.45rem; background: transparent; color: var(--muted); font-size: 0.78rem; }

#score-add {
  position: absolute;
  right: 0.6rem;
  top: -0.8rem;
  color: var(--cyan);
  font-size: 0.9rem;
  font-style: normal;
  font-weight: 800;
  opacity: 0;
  pointer-events: none;
}

#score-add.pop { animation: score-pop 650ms ease-out; }

.game-panel {
  padding: 0.9rem;
  border: 1px solid var(--line);
  border-radius: 1.6rem;
  background: var(--panel);
  box-shadow: 0 1.8rem 5rem rgba(0, 0, 0, 0.42), inset 0 1px rgba(255, 255, 255, 0.05);
  backdrop-filter: blur(22px);
}

.game-toolbar {
  min-height: 3.2rem;
  padding: 0 0.15rem 0.85rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.75rem;
}

.game-toolbar p {
  margin: 0;
  color: var(--muted);
  font-size: 0.92rem;
  line-height: 1.4;
}

button {
  min-height: 2.75rem;
  padding: 0 1rem;
  border: 0;
  border-radius: 0.8rem;
  background: var(--cyan);
  color: #06110f;
  font-weight: 850;
  cursor: pointer;
  -webkit-tap-highlight-color: transparent;
  transition: transform 140ms ease, filter 140ms ease;
}

button:active { transform: scale(0.96); }
button:focus-visible { outline: 3px solid rgba(111, 255, 233, 0.45); outline-offset: 3px; }

.board-frame { position: relative; }

.board {
  width: 100%;
  aspect-ratio: 1;
  padding: var(--gap);
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  grid-template-rows: repeat(4, 1fr);
  gap: var(--gap);
  border: 1px solid rgba(255, 255, 255, 0.07);
  border-radius: 1.15rem;
  background: rgba(2, 6, 18, 0.72);
  box-shadow: inset 0 0 3rem rgba(0, 0, 0, 0.38);
  touch-action: none;
  user-select: none;
}

.tile {
  display: grid;
  place-items: center;
  border-radius: clamp(0.6rem, 2.8vw, 0.9rem);
  background: var(--cell);
  color: var(--ink);
  font-size: clamp(1.65rem, 9vw, 3.1rem);
  font-weight: 900;
  letter-spacing: -0.06em;
  box-shadow: inset 0 1px rgba(255, 255, 255, 0.08);
  transition: background 160ms ease, color 160ms ease, box-shadow 160ms ease;
}

.tile:not([data-value="0"]) { animation: tile-in 160ms ease-out; }
.tile[data-value="2"] { background: #212c47; }
.tile[data-value="4"] { background: #263b57; }
.tile[data-value="8"] { background: #245c69; color: #dbfffa; }
.tile[data-value="16"] { background: #147d7b; color: white; }
.tile[data-value="32"] { background: #128e79; color: white; }
.tile[data-value="64"] { background: #0aa66f; color: #021d14; }
.tile[data-value="128"] { background: #514a9d; color: white; font-size: clamp(1.45rem, 7.5vw, 2.55rem); }
.tile[data-value="256"] { background: #6b4eb2; color: white; font-size: clamp(1.45rem, 7.5vw, 2.55rem); }
.tile[data-value="512"] { background: #8143be; color: white; font-size: clamp(1.45rem, 7.5vw, 2.55rem); }
.tile[data-value="1024"] { background: #a337b4; color: white; font-size: clamp(1.2rem, 6.3vw, 2.15rem); }
.tile[data-value="2048"] { background: linear-gradient(145deg, #6fffe9, #8f7cff); color: #07101b; font-size: clamp(1.2rem, 6.3vw, 2.15rem); box-shadow: 0 0 2.2rem rgba(111, 255, 233, 0.34); }
.tile[data-large="true"] { background: #d531a4; color: white; font-size: clamp(1.1rem, 5.6vw, 1.9rem); }

.game-message {
  position: absolute;
  inset: 0;
  z-index: 2;
  padding: 1.25rem;
  display: grid;
  place-items: center;
  border-radius: 1.15rem;
  background: rgba(4, 8, 20, 0.82);
  backdrop-filter: blur(12px);
  animation: veil-in 200ms ease-out;
}

.game-message[hidden] { display: none; }

.message-card {
  width: min(100%, 20rem);
  padding: 1.5rem;
  border: 1px solid var(--line);
  border-radius: 1.25rem;
  background: #11182a;
  text-align: center;
  box-shadow: 0 1rem 3rem rgba(0, 0, 0, 0.4);
}

.message-kicker {
  margin: 0;
  color: var(--cyan);
  font-size: 0.75rem;
  font-weight: 800;
  letter-spacing: 0.15em;
}

.message-card h2 { margin: 0.35rem 0 0.4rem; font-size: 2rem; }
.message-card > p:last-of-type { margin: 0 0 1.2rem; color: var(--muted); line-height: 1.5; }
.message-actions { display: flex; justify-content: center; gap: 0.65rem; }
.secondary-action { background: #252d42; color: var(--ink); }

.auth-modal {
  position: fixed;
  inset: 0;
  z-index: 10;
  padding: 1rem;
  display: grid;
  place-items: center;
  background: rgba(2, 5, 14, 0.8);
  backdrop-filter: blur(14px);
}

.auth-card {
  position: relative;
  width: min(100%, 24rem);
  padding: 1.5rem;
  border: 1px solid var(--line);
  border-radius: 1.35rem;
  background: #11182a;
  box-shadow: 0 1.5rem 5rem rgba(0, 0, 0, 0.55);
}

.auth-card h2 { margin: 0.35rem 0 1rem; font-size: 2rem; }
.icon-action {
  position: absolute;
  top: 0.7rem;
  right: 0.7rem;
  width: 2.4rem;
  min-height: 2.4rem;
  padding: 0;
  background: transparent;
  color: var(--muted);
  font-size: 1.5rem;
}
.auth-tabs { display: grid; grid-template-columns: 1fr 1fr; gap: 0.35rem; margin-bottom: 1rem; padding: 0.25rem; border-radius: 0.85rem; background: rgba(0, 0, 0, 0.22); }
.auth-tab { min-height: 2.45rem; background: transparent; color: var(--muted); }
.auth-tab.active { background: #252d42; color: var(--ink); }
.auth-card form { display: grid; gap: 0.55rem; }
.auth-card label { color: var(--muted); font-size: 0.78rem; font-weight: 700; }
.auth-card input {
  width: 100%;
  min-height: 3rem;
  margin-bottom: 0.35rem;
  padding: 0 0.85rem;
  border: 1px solid var(--line);
  border-radius: 0.8rem;
  outline: none;
  background: rgba(0, 0, 0, 0.25);
  color: var(--ink);
  font: inherit;
}
.auth-card input:focus { border-color: var(--cyan); box-shadow: 0 0 0 3px rgba(111, 255, 233, 0.12); }
.auth-error { margin: 0 0 0.25rem; color: #ff8fa3; font-size: 0.8rem; line-height: 1.4; }
.auth-note { margin: 0.9rem 0 0; color: var(--muted); font-size: 0.72rem; line-height: 1.5; }

footer {
  padding: 0 0.2rem;
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  color: #778198;
  font-size: 0.78rem;
}

kbd {
  margin-right: 0.12rem;
  padding: 0.08rem 0.22rem;
  border: 1px solid var(--line);
  border-radius: 0.25rem;
  background: rgba(255, 255, 255, 0.05);
  font: inherit;
}

@keyframes tile-in { from { opacity: 0.55; transform: scale(0.84); } }
@keyframes veil-in { from { opacity: 0; } }
@keyframes score-pop {
  0% { opacity: 0; transform: translateY(0); }
  25% { opacity: 1; }
  100% { opacity: 0; transform: translateY(-1.3rem); }
}

@media (max-height: 650px) {
  .app-shell { justify-content: flex-start; gap: 0.9rem; }
  .eyebrow { display: none; }
  h1 { font-size: 3.4rem; }
  .game-panel { padding: 0.72rem; }
  .game-toolbar { min-height: 2.8rem; padding-bottom: 0.65rem; }
  footer { display: none; }
}

@media (max-width: 390px) {
  .app-shell { padding-left: 0.8rem; padding-right: 0.8rem; }
  .game-panel { padding: 0.72rem; }
  .game-toolbar p { max-width: 11rem; }
  footer span:first-child { display: none; }
  footer { justify-content: flex-end; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation-duration: 0.01ms !important; transition-duration: 0.01ms !important; }
}