:root{
    --bg:#0b0c1a;
    --bg2:#151833;
    --tile:#1f2450;
    --tile-hover:#2c3268;
    --accent:#6ee7d8;
    --accent2:#c084fc;
    --text:#e7e9f7;
  }
  *{box-sizing:border-box;}
  html,body{
    margin:0;padding:0;height:100%;
    font-family:'Space Mono','Courier New',monospace;
    background:radial-gradient(circle at 20% 10%, #1a1f47 0%, var(--bg) 60%);
    color:var(--text);
    overflow:hidden;
  }
  #stars{
    position:fixed;inset:0;z-index:0;pointer-events:none;
  }
  #app{
    position:relative;z-index:1;
    display:flex;flex-direction:column;
    height:100vh;width:100vw;
    align-items:center;
  }
  header{
    padding:calc(env(safe-area-inset-top,0px)+14px) 20px 6px;
    text-align:center;
    flex-shrink:0;
  }
  h1{
    margin:0;
    font-size:clamp(18px,4vw,28px);
    letter-spacing:3px;
    font-weight:700;
    color:var(--accent);
    text-transform:uppercase;
  }
  .subtitle{
    margin-top:4px;
    font-size:clamp(10px,2vw,13px);
    color:var(--accent2);
    opacity:0.8;
    letter-spacing:2px;
  }
  #hud{
    display:flex;gap:22px;justify-content:center;
    margin:10px 0 4px;
    font-size:clamp(11px,2.2vw,14px);
    flex-shrink:0;
  }
  #hud span b{color:var(--accent);}
  #board-wrap{
    flex:1;width:100%;
    display:flex;align-items:center;justify-content:center;
    padding:8px 12px;
    min-height:0;
  }
  #board{
    position:relative;
    display:grid;
    grid-template-columns:repeat(4,1fr);
    grid-template-rows:repeat(4,1fr);
    gap:6px;
    width:min(90vw, 74vh, 560px);
    height:min(90vw, 74vh, 560px);
    padding:8px;
    background:var(--bg2);
    border-radius:16px;
    box-shadow:0 0 40px rgba(110,231,216,0.08), inset 0 0 20px rgba(0,0,0,0.4);
  }
  .tile{
    background:linear-gradient(145deg,var(--tile),#161a3d);
    border-radius:10px;
    display:flex;align-items:center;justify-content:center;
    font-size:clamp(18px,5vw,32px);
    font-weight:700;
    color:var(--accent);
    cursor:pointer;
    transition:background 0.15s, transform 0.15s;
    box-shadow:0 2px 0 rgba(255,255,255,0.04) inset, 0 4px 10px rgba(0,0,0,0.4);
    user-select:none;
  }
  .tile:hover{background:linear-gradient(145deg,var(--tile-hover),#1c2150);}
  .tile:active{transform:scale(0.95);}
  .tile.empty{
    background:transparent;
    box-shadow:none;
    cursor:default;
  }
  @keyframes tileCorrect{
    0%{box-shadow:0 0 0 0 rgba(110,231,216,0.7), 0 2px 0 rgba(255,255,255,0.04) inset, 0 4px 10px rgba(0,0,0,0.4);}
    60%{box-shadow:0 0 20px 6px rgba(110,231,216,0.5), 0 2px 0 rgba(255,255,255,0.04) inset, 0 4px 10px rgba(0,0,0,0.4);}
    100%{box-shadow:0 2px 0 rgba(255,255,255,0.04) inset, 0 4px 10px rgba(0,0,0,0.4);}
  }
  .tile.correct-move{animation:tileCorrect 0.45s ease-out;}
  .tile.in-place{
    background:linear-gradient(145deg,#1f5a52,#173f3a);
    color:#6ee7d8;
    box-shadow:0 0 0 2px rgba(110,231,216,0.6) inset, 0 2px 0 rgba(255,255,255,0.04) inset, 0 4px 10px rgba(0,0,0,0.4);
  }
  @keyframes boardShake{
    0%,100%{transform:translateX(0);}
    20%{transform:translateX(-6px);}
    40%{transform:translateX(5px);}
    60%{transform:translateX(-4px);}
    80%{transform:translateX(3px);}
  }
  #board.shake{animation:boardShake 0.35s ease-in-out;}
  @keyframes solvedGlow{
    0%,100%{box-shadow:0 0 40px rgba(110,231,216,0.08), inset 0 0 20px rgba(0,0,0,0.4);}
    50%{box-shadow:0 0 60px rgba(110,231,216,0.4), inset 0 0 20px rgba(0,0,0,0.4);}
  }
  #board.solved{animation:solvedGlow 0.8s ease-in-out 2;}
  footer{
    flex-shrink:0;
    padding:8px 0 calc(env(safe-area-inset-bottom,0px)+14px);
    display:flex;gap:14px;
  }
  button{
    font-family:inherit;
    background:var(--accent);
    color:#0b0c1a;
    border:none;
    padding:10px 22px;
    border-radius:24px;
    font-size:13px;
    letter-spacing:1px;
    cursor:pointer;
    font-weight:700;
    text-transform:uppercase;
    transition:transform 0.15s, background 0.2s;
  }
  button:hover{background:var(--accent2);}
  button:active{transform:scale(0.96);}
  .ghost-btn{
    background:transparent;
    color:var(--accent);
    border:1px solid var(--accent);
  }
  .ghost-btn:hover{background:rgba(110,231,216,0.08);color:var(--accent);}

  .overlay{
    position:fixed;inset:0;
    background:rgba(5,6,15,0.7);
    backdrop-filter:blur(4px);
    display:flex;align-items:center;justify-content:center;
    z-index:20;padding:20px;
  }
  .panel{
    background:var(--bg2);
    border:1px solid rgba(110,231,216,0.2);
    border-radius:18px;
    padding:32px 28px;
    max-width:420px;width:100%;
    text-align:center;
    box-shadow:0 20px 60px rgba(0,0,0,0.6), 0 0 30px rgba(110,231,216,0.08);
    position:relative;
    overflow:hidden;
    animation:panelIn 0.5s ease-out;
  }
  @keyframes panelIn{
    from{opacity:0;transform:translateY(14px) scale(0.97);}
    to{opacity:1;transform:translateY(0) scale(1);}
  }
  .panel::before{
    content:"";
    position:absolute;top:-50%;left:-20%;
    width:160%;height:140%;
    background:radial-gradient(circle at 30% 20%, rgba(192,132,252,0.15), transparent 55%);
    pointer-events:none;
  }
  .badge-icon{
    font-size:40px;margin-bottom:6px;display:inline-block;
    animation:spin 6s linear infinite;
  }
  @keyframes spin{
    from{transform:rotate(0deg);}
    to{transform:rotate(360deg);}
  }
  #start-btn{
    animation:startPulse 2.2s ease-in-out infinite;
    font-size:14px;padding:12px 30px;
  }
  @keyframes startPulse{
    0%,100%{box-shadow:0 0 0 0 rgba(110,231,216,0.5);}
    50%{box-shadow:0 0 0 10px rgba(110,231,216,0);}
  }
  .panel h2{
    margin:0 0 10px;
    letter-spacing:2px;
    color:var(--accent);
    font-size:22px;
    text-transform:uppercase;
  }
  .panel p{
    font-size:13.5px;line-height:1.6;opacity:0.85;margin:0 0 20px;
  }
  .panel .steps{
    text-align:left;font-size:13px;line-height:1.7;
    margin:0 0 22px;opacity:0.9;
  }
  .panel .steps li{margin-bottom:6px;}
  .legal-links{margin-top:18px;font-size:11px;opacity:0.55;}
  .legal-links a{color:var(--accent2);text-decoration:underline;margin:0 6px;}
  .hidden{display:none !important;}