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

  :root{
    /* night theme — light blue-grey page chrome (like Tic Tac Toe) + dark game panels */
    --surface:#28344f;--surface2:#33405e;--board:#243150;
    --border:#42517a;--text:#eef3fc;--muted:#aab9d6;
    --page:#dde3f1;--page-surface:#eaeef7;--page-surface2:#d6ddee;
    --page-ink:#1c2436;--page-muted:#4a5570;--page-border:#bfc7db;
    --accent:#7c5cff;--accent2:#22d3ee;
    --accent-dim:rgba(124,92,255,0.16);--accent-glow:rgba(124,92,255,0.45);
    --empty-cell:rgba(255,255,255,0.07);
    --shadow:0 10px 30px rgba(0,0,0,0.45);
    --on-accent:#ffffff;
    color-scheme:light;
  }
  :root[data-theme="light"]{
    /* light theme — cream chrome + light board (classic 2048) */
    --surface:#ffffff;--surface2:#f1ede0;--board:#bbada0;
    --border:#d8cfc0;--text:#3a3528;--muted:#7c7363;
    --page:#faf8ef;--page-surface:#fffdf7;--page-surface2:#f1ede0;
    --page-ink:#3a3528;--page-muted:#7c7363;--page-border:#e4dccb;
    --accent:#6d4dff;--accent2:#0891b2;
    --accent-dim:rgba(109,77,255,0.12);--accent-glow:rgba(109,77,255,0.28);
    --empty-cell:rgba(238,228,218,0.55);
    --shadow:0 8px 24px rgba(58,53,40,0.12);
    --on-accent:#ffffff;
    color-scheme:light;
  }

  html,body{background:var(--page);color:var(--page-ink);font-family:'Space Grotesk',sans-serif;}

  /* ---- shared shell ---- */
  .site-nav-bar{background:var(--page-surface);border-bottom:1px solid var(--page-border);display:flex;align-items:center;justify-content:space-between;padding:0 24px;height:56px;position:sticky;top:0;z-index:200;width:100%;}
  .site-logo{display:flex;align-items:center;gap:8px;font-family:'Orbitron',sans-serif;font-size:1rem;font-weight:700;color:var(--accent);letter-spacing:.06em;text-decoration:none;text-shadow:0 0 14px var(--accent-glow);}
  .site-logo img{width:22px;height:22px;}
  .site-nav{display:flex;align-items:center;gap:6px;}
  .nav-link{display:none;align-items:center;justify-content:center;min-width:90px;font-size:.875rem;font-weight:600;padding:8px 12px;border:1.5px solid var(--page-border);border-radius:9px;color:var(--page-ink);background:transparent;font-family:'Space Grotesk',sans-serif;text-decoration:none;transition:background .18s,border-color .18s,color .18s,transform .1s;}
  .nav-link:hover{background:var(--accent);border-color:var(--accent);color:var(--on-accent);transform:translateY(-1px);}
  .nav-link.active{background:var(--accent);border-color:var(--accent);color:var(--on-accent);}
  .nav-hamburger{display:flex;align-items:center;gap:6px;background:none;border:1px solid var(--page-border);cursor:pointer;padding:6px 12px;border-radius:9px;font-size:.85rem;font-weight:600;color:var(--page-ink);font-family:'Space Grotesk',sans-serif;transition:background .2s;min-height:38px;}
  @media(min-width:640px){.site-nav .nav-link{display:inline-flex;}.nav-hamburger{display:none;}.nav-mobile-menu{display:none !important;}}
  .nav-hamburger:hover{background:var(--page-surface2);}
  .nav-mobile-menu{display:none;flex-direction:column;background:var(--page-surface);border-bottom:1px solid var(--page-border);padding:10px 16px 14px;gap:8px;position:sticky;top:56px;z-index:199;}
  .nav-mobile-menu.open{display:flex;}
  .nav-mobile-link{display:block;text-align:center;text-decoration:none;font-family:'Space Grotesk',sans-serif;font-size:1rem;font-weight:600;color:var(--page-ink);background:var(--page-surface2);border:1.5px solid var(--page-border);border-radius:9px;padding:13px 16px;transition:background .18s,border-color .18s,color .18s;}
  .nav-mobile-link:hover,.nav-mobile-link.active{background:var(--accent);border-color:var(--accent);color:var(--on-accent);}
  .theme-toggle{display:inline-flex;align-items:center;justify-content:center;width:38px;height:38px;min-width:38px;border:1.5px solid var(--page-border);border-radius:9px;background:transparent;color:var(--accent);cursor:pointer;transition:background .18s,border-color .18s,transform .1s;margin-right:6px;}
  .theme-toggle:hover{border-color:var(--accent);background:var(--accent-dim);transform:translateY(-1px);}
  .theme-toggle svg{width:18px;height:18px;}
  .theme-toggle .ti-moon{display:none;}
  :root[data-theme="light"] .theme-toggle .ti-sun{display:none;}
  :root[data-theme="light"] .theme-toggle .ti-moon{display:inline-block;}

  /* ---- game layout ---- */
  #wrap{padding:24px 16px 8px;min-height:62vh;}
  #inner{display:flex;flex-direction:column;align-items:center;gap:16px;max-width:480px;margin:0 auto;}
  .game-logo{display:flex;align-items:center;justify-content:center;gap:10px;font-family:'Orbitron',sans-serif;font-size:clamp(1.7rem,6vw,2.5rem);font-weight:900;letter-spacing:.06em;color:var(--accent);text-shadow:0 0 22px var(--accent-glow);}
  .game-logo img{width:clamp(28px,6vw,40px);height:clamp(28px,6vw,40px);}
  .tagline{font-size:.72rem;color:var(--page-muted);letter-spacing:.18em;text-transform:uppercase;margin-top:5px;text-align:center;}

  .topbar{width:100%;display:flex;align-items:stretch;justify-content:space-between;gap:10px;}
  .scores{display:flex;gap:10px;}
  .score-box{background:var(--surface);border:1px solid var(--border);border-radius:12px;padding:8px 16px;text-align:center;min-width:92px;display:flex;flex-direction:column;justify-content:center;}
  .score-label{font-size:.58rem;letter-spacing:.14em;text-transform:uppercase;color:var(--muted);}
  .score-value{font-family:'Orbitron',sans-serif;font-size:1.3rem;font-weight:700;line-height:1.2;color:var(--text);position:relative;}
  .score-add{position:absolute;left:50%;top:0;transform:translateX(-50%);color:var(--accent2);font-size:.95rem;font-weight:700;opacity:0;animation:floatUp .6s ease forwards;pointer-events:none;}
  @keyframes floatUp{0%{opacity:1;transform:translate(-50%,0);}100%{opacity:0;transform:translate(-50%,-26px);}}
  .btn-new{align-self:stretch;background:var(--accent);color:var(--on-accent);border:none;border-radius:12px;padding:0 18px;font-family:'Orbitron',sans-serif;font-size:.8rem;font-weight:700;letter-spacing:.06em;cursor:pointer;transition:filter .2s,box-shadow .2s,transform .1s;box-shadow:0 0 22px var(--accent-glow);min-height:44px;}
  .btn-new:hover{filter:brightness(1.08);box-shadow:0 0 38px var(--accent-glow);transform:translateY(-1px);}
  /* Phones: 4 score boxes + New Game can't fit one row. Let the boxes shrink and
     wrap New Game onto its own full-width row below the scores. */
  @media(max-width:520px){
    .topbar{flex-wrap:wrap;}
    .scores{flex:1 1 100%;gap:6px;}
    .score-box{min-width:0;flex:1;padding:8px 8px;}
    .btn-new{flex:1 1 100%;padding:10px 18px;}
  }

  /* ---- board ---- */
  #board-wrap{width:100%;position:relative;}
  .board{--gap:clamp(8px,2.4vw,13px);position:relative;width:100%;max-width:480px;aspect-ratio:1;margin:0 auto;background:var(--board);border-radius:14px;padding:var(--gap);box-shadow:var(--shadow);touch-action: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(--empty-cell);border-radius:8px;}
  .tiles{position:absolute;inset:var(--gap);}
  .tile{position:absolute;width:calc((100% - 3*var(--gap))/4);height:calc((100% - 3*var(--gap))/4);transform:translate(calc(var(--c)*(100% + var(--gap))),calc(var(--r)*(100% + var(--gap))));transition:transform .12s ease-in-out;will-change:transform;}
  .tile-inner{width:100%;height:100%;border-radius:8px;display:flex;align-items:center;justify-content:center;font-family:'Orbitron',sans-serif;font-weight:900;line-height:1;font-size:clamp(1.4rem,7.4vw,2.2rem);color:#fff;background:#2a3550;}
  .tile.len3 .tile-inner{font-size:clamp(1.1rem,5.8vw,1.75rem);}
  .tile.len4 .tile-inner{font-size:clamp(.85rem,4.7vw,1.4rem);}
  .tile.len5 .tile-inner{font-size:clamp(.7rem,3.9vw,1.15rem);}
  .tile.new .tile-inner{animation:appear .16s ease;}
  .tile.merged .tile-inner{animation:pop .18s ease;}
  @keyframes appear{0%{transform:scale(0);opacity:0;}100%{transform:scale(1);opacity:1;}}
  @keyframes pop{0%{transform:scale(1);}50%{transform:scale(1.18);}100%{transform:scale(1);}}

  /* tile color ramp — cool → hot → gold */
  .tile[data-v="2"]    .tile-inner{background:#eee4da;color:#2f2a1d;}
  :root[data-theme="light"] .tile[data-v="2"] .tile-inner{background:#3c486b;color:#dce6f7;}
  .tile[data-v="4"]    .tile-inner{background:#3f5d8c;color:#e6f0ff;}
  .tile[data-v="8"]    .tile-inner{background:#1d6fa5;}
  .tile[data-v="16"]   .tile-inner{background:#2563eb;}
  .tile[data-v="32"]   .tile-inner{background:#4f46e5;}
  .tile[data-v="64"]   .tile-inner{background:#7c3aed;}
  .tile[data-v="128"]  .tile-inner{background:#9d2bdb;box-shadow:0 0 16px rgba(157,43,219,.5);}
  .tile[data-v="256"]  .tile-inner{background:#c026d3;box-shadow:0 0 18px rgba(192,38,211,.55);}
  .tile[data-v="512"]  .tile-inner{background:#db2777;box-shadow:0 0 20px rgba(219,39,119,.6);}
  .tile[data-v="1024"] .tile-inner{background:#ef6c00;box-shadow:0 0 24px rgba(239,108,0,.6);}
  .tile[data-v="2048"] .tile-inner{background:#f5b50a;color:#1a1304;box-shadow:0 0 32px rgba(245,181,10,.75);}
  .tile.super .tile-inner{background:linear-gradient(135deg,#ffd34d,#fff);color:#1a1304;box-shadow:0 0 38px rgba(255,211,77,.85);}

  /* ---- controls ---- */
  #controls{width:100%;max-width:480px;display:flex;gap:12px;flex-wrap:wrap;}
  .ctl{flex:1;min-width:96px;display:flex;flex-direction:column;align-items:center;justify-content:center;gap:10px;background:linear-gradient(180deg,rgba(255,255,255,0.06),rgba(255,255,255,0)),var(--surface);border:1.5px solid var(--border);border-radius:18px;padding:16px 8px 14px;color:var(--text);font-family:'Space Grotesk',sans-serif;font-size:.84rem;font-weight:700;letter-spacing:.02em;cursor:pointer;transition:transform .14s,border-color .18s,box-shadow .18s;min-height:92px;}
  .ctl .cic{font-size:1.55rem;line-height:1;color:var(--accent);display:flex;align-items:center;justify-content:center;width:50px;height:50px;border-radius:15px;background:rgba(124,92,255,0.12);transition:background .18s,transform .14s;}
  .ctl .cic svg{display:block;}
  .ctl .cic .ic-ball{width:30px;height:30px;}
  .ctl .cic .ic-undo{width:36px;height:36px;}
  #btn-hint .cic{font-size:2rem;}
  .ctl:hover{border-color:var(--accent);color:var(--accent);transform:translateY(-3px);box-shadow:0 10px 26px var(--accent-glow);}
  .ctl:hover .cic{background:var(--accent-dim);transform:scale(1.06);}
  .ctl:active{transform:translateY(-1px);}
  .ctl:disabled{opacity:.4;cursor:default;}
  /* Auto running — glowing accent outline only; interior stays normal */
  .ctl.on{border-color:var(--accent);color:var(--accent);animation:ctlPulse 1.5s ease-in-out infinite;}
  @keyframes ctlPulse{0%,100%{box-shadow:0 0 0 1.5px var(--accent),0 0 14px var(--accent-glow);}50%{box-shadow:0 0 0 1.5px var(--accent),0 0 30px var(--accent-glow);}}
  @media(prefers-reduced-motion:reduce){.ctl.on{animation:none;box-shadow:0 0 0 1.5px var(--accent),0 0 18px var(--accent-glow);}}
  #btn-auto{background:#2563eb;border-color:#2563eb;color:#fff;}
  #btn-auto .cic{background:rgba(255,255,255,.18);}
  #btn-auto:hover{border-color:#1d4ed8;color:#fff;box-shadow:0 10px 26px rgba(37,99,235,.45);}
  #btn-auto.on{background:#1d4ed8;border-color:#1d4ed8;color:#fff;animation:none;box-shadow:inset 0 0 0 2px rgba(255,255,255,.6);}

  #hint-msg{width:100%;max-width:480px;background:var(--surface);border:1px solid var(--accent);border-radius:10px;padding:0 14px;color:var(--text);font-size:.86rem;line-height:1.5;overflow:hidden;max-height:0;opacity:0;transition:max-height .25s,opacity .25s,padding .25s;}
  #hint-msg.show{padding:12px 14px;max-height:140px;opacity:1;}
  #hint-msg strong{color:#ffffff;}
  :root[data-theme="light"] #hint-msg strong{color:var(--accent);}

  /* ---- overlay ---- */
  #overlay{display:none;position:absolute;inset:0;border-radius:14px;background:rgba(28,39,66,0.86);backdrop-filter:blur(3px);align-items:center;justify-content:center;flex-direction:column;text-align:center;padding:24px;z-index:5;}
  :root[data-theme="light"] #overlay{background:rgba(250,248,239,0.86);}
  #overlay.show{display:flex;}
  .ov-icon{font-size:3rem;margin-bottom:8px;}
  .ov-title{font-family:'Orbitron',sans-serif;font-size:1.8rem;font-weight:900;margin-bottom:6px;color:var(--accent);text-shadow:0 0 22px var(--accent-glow);}
  #overlay.lose .ov-title{color:var(--text);}
  .ov-sub{color:var(--muted);font-size:.92rem;margin-bottom:22px;line-height:1.6;max-width:280px;}
  .ov-sub b{color:var(--accent);}
  .ov-btns{display:flex;flex-direction:column;gap:10px;width:200px;max-width:100%;}
  .ov-btn{padding:13px;background:var(--accent);color:var(--on-accent);border:none;border-radius:10px;font-family:'Orbitron',sans-serif;font-size:.82rem;font-weight:700;letter-spacing:.06em;cursor:pointer;transition:filter .2s,transform .1s;min-height:44px;}
  .ov-btn:hover{filter:brightness(1.08);transform:translateY(-1px);}
  .ov-btn.ghost{background:transparent;border:1px solid var(--border);color:var(--muted);}
  .ov-btn.ghost:hover{border-color:var(--accent);color:var(--accent);}

  /* ---- info section ---- */
  .info{background:var(--page);max-width:760px;margin:0 auto;padding:48px 20px 64px;font-family:'Space Grotesk',sans-serif;}
  .info h2{font-family:'Orbitron',sans-serif;font-size:.9rem;font-weight:700;color:var(--accent);letter-spacing:.12em;text-transform:uppercase;margin:0 0 14px;}
  .info p,.info li{font-size:.92rem;line-height:1.8;color:var(--page-ink);opacity:.86;margin:0 0 10px;}
  .info ul,.info ol{padding-left:20px;margin:0 0 10px;}
  .info li{margin:0 0 6px;}
  .info li strong{color:var(--accent);opacity:1;}
  .info a{color:var(--accent);text-decoration:none;}
  .info a:hover{text-decoration:underline;}
  .info-grid{display:grid;grid-template-columns:1fr 1fr;gap:40px;}
  .info-divider{width:100%;height:1px;background:var(--page-border);margin:36px 0;}
  @media(max-width:600px){.info-grid{grid-template-columns:1fr;gap:28px;}}

  footer{text-align:center;padding:32px 24px;border-top:1px solid var(--page-border);font-size:.82rem;color:var(--page-muted);background:var(--page);}
  footer a{color:var(--accent);text-decoration:none;}
  footer a:hover{text-decoration:underline;}

  @media(prefers-reduced-motion:reduce){.tile{transition:none;}.tile.new .tile-inner,.tile.merged .tile-inner{animation:none;}}

  /* ---- Solve My Board ---- */
  .sb-grid{display:grid;grid-template-columns:repeat(4,1fr);gap:6px;max-width:320px;margin:1rem 0;}
  .sb-cell{aspect-ratio:1;border:2px solid #bbada0;border-radius:6px;background:#cdc1b4;
    font:700 1.1rem/1 system-ui,sans-serif;color:#776e65;cursor:pointer;display:flex;
    align-items:center;justify-content:center;user-select:none;}
  .sb-cell[data-v="0"]{color:transparent;}
  .sb-controls{display:flex;gap:0.5rem;flex-wrap:wrap;margin:0.5rem 0;}
  .sb-btn{padding:0.5rem 1rem;border:1px solid #bbada0;border-radius:6px;background:#fff;
    color:#776e65;font-weight:600;cursor:pointer;}
  .sb-btn-primary{background:#8f7a66;color:#f9f6f2;border-color:#8f7a66;}
  .sb-result{margin-top:0.75rem;min-height:1.5rem;font-size:0.95rem;line-height:1.6;color:var(--page-ink);}
  .sb-move{font-weight:900;font-size:1.2rem;color:var(--accent);}
  .sb-scores{margin:0.5rem 0 0;color:var(--page-muted);font-size:0.85rem;}