@import url('https://fonts.googleapis.com/css2?family=Orbitron:wght@400;600;700;900&family=Exo+2:wght@300;400;500&display=swap');

  :root {
    --bg-deep: #030610;
    --bg-mid: #070d1e;
    --bg-surface: #0d1530;
    --accent-cyan: #00e5ff;
    --accent-gold: #ffd060;
    --accent-violet: #b06aff;
    --accent-green: #39ff8c;
    --text-bright: #e8f4ff;
    --text-dim: #5a7a9e;
    --tile-1: #1a3a6e;
    --tile-2: #0d2850;
    --tile-border: #1e4080;
    --glow-cyan: 0 0 12px rgba(0,229,255,0.6), 0 0 30px rgba(0,229,255,0.2);
    --glow-gold: 0 0 12px rgba(255,208,96,0.6), 0 0 30px rgba(255,208,96,0.2);
    --glow-violet: 0 0 12px rgba(176,106,255,0.5), 0 0 25px rgba(176,106,255,0.2);
    --radius: 10px;
    --transition: 0.2s cubic-bezier(0.34,1.56,0.64,1);
  }

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

  html, body {
    height: 100%;
    background: var(--bg-deep);
    color: var(--text-bright);
    font-family: 'Exo 2', sans-serif;
    overflow-x: hidden;
  }

  /* ===== STARFIELD ===== */
  #starfield {
    position: fixed; inset: 0; z-index: 0; pointer-events: none;
    overflow: hidden;
  }
  .star {
    position: absolute;
    background: #fff;
    border-radius: 50%;
    animation: twinkle var(--dur, 3s) ease-in-out infinite;
    animation-delay: var(--del, 0s);
    opacity: 0.4;
  }
  @keyframes twinkle {
    0%,100% { opacity: 0.15; transform: scale(1); }
    50% { opacity: 0.9; transform: scale(1.3); }
  }
  .nebula {
    position: absolute;
    border-radius: 50%;
    filter: blur(60px);
    opacity: 0.06;
    animation: drift 20s ease-in-out infinite alternate;
  }
  @keyframes drift {
    from { transform: translate(0,0) scale(1); }
    to { transform: translate(30px, 20px) scale(1.05); }
  }

  /* ===== LAYOUT ===== */
  #app {
    position: relative; z-index: 1;
    min-height: 100vh;
    display: flex; flex-direction: column;
  }

  /* ===== SCREENS ===== */
  .screen {
    display: none; flex: 1; flex-direction: column;
    align-items: center; justify-content: center;
    padding: 20px 16px 32px;
    min-height: 100vh;
  }
  .screen.active { display: flex; }

  /* ===== HOME ===== */
  .home-logo {
    text-align: center;
    margin-bottom: 32px;
    animation: fadeDown 0.7s ease both;
  }
  .home-logo .planet {
    width: 90px; height: 90px;
    margin: 0 auto 16px;
    position: relative;
  }
  .planet-body {
    width: 90px; height: 90px;
    border-radius: 50%;
    background: radial-gradient(circle at 35% 35%, #3a8cff, #0a2060 60%, #06133d);
    box-shadow: var(--glow-cyan), inset -10px -10px 30px rgba(0,0,0,0.5);
    position: relative;
    overflow: hidden;
    animation: spin 20s linear infinite;
  }
  @keyframes spin { to { transform: rotate(360deg); } }
  .planet-ring {
    position: absolute;
    width: 130px; height: 28px;
    border: 3px solid rgba(0,229,255,0.5);
    border-radius: 50%;
    top: 50%; left: 50%;
    transform: translate(-50%, -50%) rotateX(70deg);
    box-shadow: 0 0 12px rgba(0,229,255,0.4);
    pointer-events: none;
  }
  .home-title {
    font-family: 'Orbitron', monospace;
    font-weight: 900;
    font-size: clamp(2rem, 8vw, 3.2rem);
    letter-spacing: 0.12em;
    background: linear-gradient(135deg, var(--accent-cyan) 0%, var(--accent-violet) 60%, var(--accent-gold) 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    line-height: 1.1;
  }
  .home-subtitle {
    font-size: 0.95rem;
    letter-spacing: 0.25em;
    color: var(--text-dim);
    margin-top: 6px;
    text-transform: uppercase;
  }

  @keyframes fadeDown {
    from { opacity: 0; transform: translateY(-30px); }
    to { opacity: 1; transform: translateY(0); }
  }

  /* ===== BUTTONS ===== */
  .btn {
    display: inline-flex; align-items: center; justify-content: center;
    gap: 8px;
    font-family: 'Orbitron', monospace;
    font-size: 0.85rem;
    font-weight: 600;
    letter-spacing: 0.1em;
    text-transform: uppercase;
    border: none; border-radius: var(--radius);
    cursor: pointer;
    transition: transform 0.15s ease, box-shadow 0.15s ease, background 0.15s ease;
    text-decoration: none;
    -webkit-tap-highlight-color: transparent;
    user-select: none;
  }
  .btn:active { transform: scale(0.95) !important; }

  .btn-primary {
    background: linear-gradient(135deg, #0077cc, #0044aa);
    color: var(--accent-cyan);
    box-shadow: var(--glow-cyan), inset 0 1px 0 rgba(255,255,255,0.1);
    padding: 16px 40px;
    font-size: 1rem;
    width: 100%; max-width: 300px;
    border: 1px solid rgba(0,229,255,0.3);
  }
  .btn-primary:hover { transform: translateY(-2px); box-shadow: 0 0 20px rgba(0,229,255,0.8), 0 0 40px rgba(0,229,255,0.3); }

  .btn-secondary {
    background: rgba(255,255,255,0.05);
    color: var(--text-dim);
    padding: 12px 28px;
    border: 1px solid rgba(255,255,255,0.1);
    font-size: 0.8rem;
    width: 100%; max-width: 300px;
  }
  .btn-secondary:hover { background: rgba(255,255,255,0.08); color: var(--text-bright); }

  .btn-icon {
    background: rgba(255,255,255,0.05);
    border: 1px solid rgba(255,255,255,0.12);
    color: var(--text-dim);
    padding: 10px 16px;
    border-radius: 8px;
    font-size: 0.75rem;
  }
  .btn-icon:hover { border-color: var(--accent-cyan); color: var(--accent-cyan); }

  .menu-buttons {
    display: flex; flex-direction: column; gap: 12px;
    width: 100%; max-width: 300px;
    animation: fadeUp 0.7s ease 0.2s both;
  }
  @keyframes fadeUp {
    from { opacity: 0; transform: translateY(20px); }
    to { opacity: 1; transform: translateY(0); }
  }

  /* ===== DIFFICULTY SELECT ===== */
  .diff-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 14px;
    width: 100%; max-width: 360px;
    animation: fadeUp 0.5s ease both;
  }
  .diff-card {
    background: var(--bg-surface);
    border: 1px solid var(--tile-border);
    border-radius: 14px;
    padding: 20px 14px;
    text-align: center;
    cursor: pointer;
    transition: transform var(--transition), border-color 0.2s, box-shadow 0.2s;
    -webkit-tap-highlight-color: transparent;
  }
  .diff-card:hover, .diff-card:focus {
    transform: translateY(-4px) scale(1.03);
    border-color: var(--accent-cyan);
    box-shadow: var(--glow-cyan);
    outline: none;
  }
  .diff-card .icon {
    font-size: 2rem;
    margin-bottom: 8px;
    display: block;
  }
  .diff-card .label {
    font-family: 'Orbitron', monospace;
    font-size: 0.8rem;
    font-weight: 700;
    letter-spacing: 0.1em;
    color: var(--accent-cyan);
  }
  .diff-card .desc {
    font-size: 0.72rem;
    color: var(--text-dim);
    margin-top: 4px;
    line-height: 1.4;
  }
  .diff-card[data-diff="easy"] { border-color: rgba(57,255,140,0.3); }
  .diff-card[data-diff="easy"] .label { color: var(--accent-green); }
  .diff-card[data-diff="easy"]:hover { border-color: var(--accent-green); box-shadow: var(--glow-cyan); }
  .diff-card[data-diff="medium"] { border-color: rgba(0,229,255,0.3); }
  .diff-card[data-diff="hard"] { border-color: rgba(176,106,255,0.3); }
  .diff-card[data-diff="hard"] .label { color: var(--accent-violet); }
  .diff-card[data-diff="hard"]:hover { border-color: var(--accent-violet); box-shadow: var(--glow-violet); }
  .diff-card[data-diff="expert"] { border-color: rgba(255,208,96,0.3); }
  .diff-card[data-diff="expert"] .label { color: var(--accent-gold); }
  .diff-card[data-diff="expert"]:hover { border-color: var(--accent-gold); box-shadow: var(--glow-gold); }

  /* ===== GAME SCREEN ===== */
  #screen-game {
    padding: 12px 12px 20px;
    justify-content: flex-start;
  }

  .game-header {
    width: 100%; max-width: 480px;
    display: flex; align-items: center; gap: 10px;
    margin-bottom: 14px;
  }
  .game-title-bar {
    flex: 1;
    font-family: 'Orbitron', monospace;
    font-size: 0.75rem;
    letter-spacing: 0.12em;
    color: var(--text-dim);
    text-transform: uppercase;
  }
  .stat-row {
    width: 100%; max-width: 480px;
    display: flex; gap: 10px;
    margin-bottom: 16px;
  }
  .stat-box {
    flex: 1;
    background: var(--bg-surface);
    border: 1px solid var(--tile-border);
    border-radius: 10px;
    padding: 8px 12px;
    text-align: center;
  }
  .stat-label {
    font-size: 0.62rem;
    letter-spacing: 0.15em;
    color: var(--text-dim);
    text-transform: uppercase;
    display: block;
  }
  .stat-value {
    font-family: 'Orbitron', monospace;
    font-size: 1.1rem;
    font-weight: 700;
    color: var(--accent-cyan);
    display: block;
    margin-top: 2px;
  }
  .stat-box.timer .stat-value { color: var(--accent-gold); }
  .stat-box.moves .stat-value { color: var(--accent-violet); }

  /* ===== PUZZLE GRID ===== */
  #puzzle-wrapper {
    width: 100%;
    max-width: 480px;
    aspect-ratio: 1;
    position: relative;
  }
  #puzzle-grid {
    width: 100%; height: 100%;
    display: grid;
    gap: 4px;
    padding: 4px;
    background: var(--bg-surface);
    border: 1px solid var(--tile-border);
    border-radius: 16px;
    box-shadow: inset 0 0 30px rgba(0,0,0,0.5), 0 0 20px rgba(0,100,200,0.1);
    touch-action: none;
  }

  .tile {
    border-radius: 8px;
    background: linear-gradient(135deg, var(--tile-1), var(--tile-2));
    border: 1px solid var(--tile-border);
    display: flex; align-items: center; justify-content: center;
    font-family: 'Orbitron', monospace;
    font-weight: 700;
    color: var(--accent-cyan);
    cursor: pointer;
    transition: transform var(--transition), box-shadow 0.15s ease, background 0.15s ease, opacity 0.15s ease;
    position: relative;
    overflow: hidden;
    -webkit-tap-highlight-color: transparent;
    user-select: none;
  }
  .tile::before {
    content: '';
    position: absolute; inset: 0;
    background: linear-gradient(135deg, rgba(255,255,255,0.08) 0%, transparent 60%);
    border-radius: inherit;
    pointer-events: none;
  }
  .tile:active { transform: scale(0.93); }
  .tile.selected {
    background: linear-gradient(135deg, #0055aa, #003080);
    border-color: var(--accent-cyan);
    box-shadow: var(--glow-cyan);
    transform: scale(1.04);
    z-index: 2;
  }
  .tile.empty {
    background: rgba(0,0,0,0.3);
    border-color: rgba(255,255,255,0.05);
    cursor: default;
    box-shadow: inset 0 0 15px rgba(0,0,0,0.5);
  }
  .tile.correct {
    border-color: var(--accent-green);
    box-shadow: 0 0 10px rgba(57,255,140,0.4);
    background: linear-gradient(135deg, #0a3322, #061a12);
  }
  .tile.correct .tile-num { color: var(--accent-green); }
  .tile.sliding {
    transition: transform 0.18s ease;
  }
  .tile-num {
    font-size: clamp(0.7rem, 3vw, 1.2rem);
    font-weight: 700;
    letter-spacing: 0.05em;
    position: relative; z-index: 1;
  }
  .tile-symbol {
    position: absolute;
    bottom: 4px; right: 6px;
    font-size: clamp(0.5rem, 2vw, 0.8rem);
    opacity: 0.4;
    color: var(--text-dim);
  }

  /* grid sizes */
  .grid-3 { grid-template-columns: repeat(3, 1fr); }
  .grid-4 { grid-template-columns: repeat(4, 1fr); }
  .grid-5 { grid-template-columns: repeat(5, 1fr); }

  /* ===== WIN SCREEN ===== */
  .win-container {
    text-align: center;
    max-width: 360px;
    animation: zoomIn 0.5s cubic-bezier(0.34,1.56,0.64,1) both;
  }
  @keyframes zoomIn {
    from { opacity: 0; transform: scale(0.7); }
    to { opacity: 1; transform: scale(1); }
  }
  .win-star {
    font-size: 4rem;
    margin-bottom: 16px;
    display: block;
    animation: starPulse 1.5s ease infinite;
  }
  .star-svg {
    width: 80px; height: 80px;
    margin: 0 auto 16px;
    display: block;
    filter: drop-shadow(0 0 16px rgba(255,208,96,0.8));
    animation: starPulse 1.5s ease infinite;
  }
  @keyframes starPulse {
    0%,100% { transform: scale(1) rotate(0deg); filter: drop-shadow(0 0 16px rgba(255,208,96,0.8)); }
    50% { transform: scale(1.12) rotate(10deg); filter: drop-shadow(0 0 30px rgba(255,208,96,1)); }
  }
  .win-title {
    font-family: 'Orbitron', monospace;
    font-size: clamp(1.6rem, 7vw, 2.4rem);
    font-weight: 900;
    background: linear-gradient(135deg, var(--accent-gold), var(--accent-cyan));
    -webkit-background-clip: text; -webkit-text-fill-color: transparent;
    background-clip: text;
    margin-bottom: 8px;
  }
  .win-sub { color: var(--text-dim); font-size: 0.9rem; margin-bottom: 28px; }
  .win-stats {
    display: flex; gap: 16px; justify-content: center;
    margin-bottom: 32px;
  }
  .win-stat {
    background: var(--bg-surface);
    border: 1px solid var(--tile-border);
    border-radius: 12px;
    padding: 14px 20px;
    min-width: 90px;
  }
  .win-stat-val {
    font-family: 'Orbitron', monospace;
    font-size: 1.4rem;
    font-weight: 700;
    color: var(--accent-gold);
    display: block;
  }
  .win-stat-lbl {
    font-size: 0.65rem;
    color: var(--text-dim);
    letter-spacing: 0.12em;
    text-transform: uppercase;
    display: block;
    margin-top: 2px;
  }
  .win-buttons { display: flex; flex-direction: column; gap: 10px; width: 100%; }

  /* ===== SCREEN TITLE ===== */
  .screen-heading {
    font-family: 'Orbitron', monospace;
    font-weight: 700;
    font-size: clamp(1.2rem, 5vw, 1.8rem);
    letter-spacing: 0.08em;
    color: var(--text-bright);
    margin-bottom: 8px;
    text-align: center;
  }
  .screen-sub {
    color: var(--text-dim);
    font-size: 0.85rem;
    margin-bottom: 28px;
    text-align: center;
    max-width: 300px;
    line-height: 1.5;
  }

  /* ===== HOW TO PLAY ===== */
  .how-list {
    width: 100%; max-width: 360px;
    list-style: none;
    display: flex; flex-direction: column; gap: 12px;
    margin-bottom: 28px;
    animation: fadeUp 0.5s ease both;
  }
  .how-list li {
    display: flex; align-items: flex-start; gap: 14px;
    background: var(--bg-surface);
    border: 1px solid var(--tile-border);
    border-radius: 12px;
    padding: 14px;
  }
  .how-num {
    font-family: 'Orbitron', monospace;
    font-size: 1.1rem;
    font-weight: 900;
    color: var(--accent-cyan);
    min-width: 28px;
    line-height: 1;
  }
  .how-text {
    font-size: 0.87rem;
    line-height: 1.5;
    color: var(--text-bright);
  }
  .how-text strong { color: var(--accent-cyan); }

  /* ===== HIGH SCORES ===== */
  .score-table {
    width: 100%; max-width: 360px;
    border-collapse: collapse;
    margin-bottom: 28px;
    animation: fadeUp 0.5s ease both;
  }
  .score-table th {
    font-family: 'Orbitron', monospace;
    font-size: 0.65rem;
    letter-spacing: 0.15em;
    color: var(--text-dim);
    text-transform: uppercase;
    padding: 8px 12px;
    text-align: left;
    border-bottom: 1px solid var(--tile-border);
  }
  .score-table td {
    font-size: 0.85rem;
    padding: 10px 12px;
    border-bottom: 1px solid rgba(255,255,255,0.04);
    color: var(--text-bright);
  }
  .score-table tr:first-child td { padding-top: 14px; }
  .score-rank {
    font-family: 'Orbitron', monospace;
    font-size: 0.75rem;
    font-weight: 700;
    color: var(--text-dim);
  }
  .score-rank.gold { color: var(--accent-gold); }
  .score-rank.silver { color: #b0c4de; }
  .score-rank.bronze { color: #cd7f32; }
  .badge {
    display: inline-block;
    font-family: 'Orbitron', monospace;
    font-size: 0.62rem;
    padding: 2px 7px;
    border-radius: 4px;
    font-weight: 700;
    letter-spacing: 0.06em;
  }
  .badge-easy { background: rgba(57,255,140,0.15); color: var(--accent-green); border: 1px solid rgba(57,255,140,0.3); }
  .badge-medium { background: rgba(0,229,255,0.12); color: var(--accent-cyan); border: 1px solid rgba(0,229,255,0.25); }
  .badge-hard { background: rgba(176,106,255,0.12); color: var(--accent-violet); border: 1px solid rgba(176,106,255,0.25); }
  .badge-expert { background: rgba(255,208,96,0.12); color: var(--accent-gold); border: 1px solid rgba(255,208,96,0.25); }

  /* ===== FOOTER ===== */
  .home-footer {
    margin-top: auto;
    padding-top: 24px;
    text-align: center;
    font-size: 0.75rem;
    color: var(--text-dim);
    animation: fadeUp 0.7s ease 0.4s both;
  }
  .home-footer a {
    color: var(--text-dim);
    text-decoration: none;
    transition: color 0.2s;
    letter-spacing: 0.05em;
  }
  .home-footer a:hover { color: var(--accent-cyan); }
  .home-footer .sep { margin: 0 10px; opacity: 0.4; }
  .home-footer .copy { margin-top: 6px; opacity: 0.5; font-size: 0.68rem; }

  /* ===== TOAST ===== */
  #toast {
    position: fixed;
    bottom: 30px; left: 50%;
    transform: translateX(-50%) translateY(80px);
    background: rgba(0,229,255,0.15);
    border: 1px solid rgba(0,229,255,0.4);
    color: var(--accent-cyan);
    font-family: 'Orbitron', monospace;
    font-size: 0.78rem;
    letter-spacing: 0.1em;
    padding: 12px 24px;
    border-radius: 30px;
    white-space: nowrap;
    z-index: 100;
    transition: transform 0.3s cubic-bezier(0.34,1.56,0.64,1), opacity 0.3s ease;
    opacity: 0;
    backdrop-filter: blur(10px);
  }
  #toast.show { transform: translateX(-50%) translateY(0); opacity: 1; }

  /* ===== PARTICLES ===== */
  .particle {
    position: fixed;
    pointer-events: none;
    border-radius: 50%;
    z-index: 50;
    animation: particleFly 1s ease-out forwards;
  }
  @keyframes particleFly {
    0% { opacity: 1; transform: translate(0,0) scale(1); }
    100% { opacity: 0; transform: translate(var(--tx), var(--ty)) scale(0); }
  }

  /* ===== PROGRESS BAR ===== */
  .progress-wrap {
    width: 100%; max-width: 480px;
    height: 4px;
    background: rgba(255,255,255,0.06);
    border-radius: 4px;
    margin-bottom: 12px;
    overflow: hidden;
  }
  .progress-bar {
    height: 100%;
    background: linear-gradient(90deg, var(--accent-cyan), var(--accent-violet));
    border-radius: 4px;
    transition: width 0.4s ease;
    box-shadow: 0 0 8px rgba(0,229,255,0.6);
  }

  /* ===== RESPONSIVE ===== */
  @media (min-width: 480px) {
    .tile-num { font-size: 1.4rem; }
    .tile-symbol { font-size: 0.9rem; }
  }
  @media (min-width: 640px) {
    .game-header { margin-bottom: 16px; }
  }