:root {
    --bg: #020617;
    --card-bg: rgba(15, 23, 42, 0.95);
    --accent: #38bdf8;
    --text: #f1f5f9;
    --cell-bg: #1e293b;
    --cell-border: #334155;
    --error: #ef4444;
    --hint: #10b981;
    --font-main: 'Montserrat', sans-serif;
    --font-display: 'Orbitron', sans-serif;
}

body {
    font-family: var(--font-main);
    background: radial-gradient(circle at center, #1e293b, #020617);
    color: var(--text);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    margin: 0;
    overflow: hidden;
}

.glass-panel {
    background: var(--card-bg);
    backdrop-filter: blur(20px);
    padding: 2.5rem;
    border-radius: 32px;
    border: 1px solid rgba(255, 255, 255, 0.1);
    box-shadow: 0 50px 100px -20px rgba(0, 0, 0, 0.8);
    width: 90%;
    max-width: 420px;
    text-align: center;
    position: relative;
}

h1 { 
    font-family: var(--font-display);
    font-weight: 900; 
    letter-spacing: 12px; 
    margin: 0.5rem 0 1.5rem 0; 
    color: white; 
    text-shadow: 0 0 15px rgba(56, 189, 248, 0.6); 
    font-size: 2.5rem;
}

select {
    font-family: var(--font-main);
    width: 100%;
    padding: 14px;
    margin: 20px 0;
    border-radius: 12px;
    background: #0f172a;
    color: white;
    border: 1px solid var(--cell-border);
    cursor: pointer;
    font-weight: 600;
}

.btn {
    font-family: var(--font-main);
    width: 100%;
    padding: 16px;
    border-radius: 16px;
    border: none;
    cursor: pointer;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 1px;
    transition: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    margin-bottom: 12px;
}

.btn-primary { background: var(--accent); color: var(--bg); }
.btn-primary:hover { transform: translateY(-2px); box-shadow: 0 10px 20px -10px var(--accent); }

.btn-outline { 
    background: transparent; 
    color: var(--accent); 
    border: 1px solid var(--accent); 
}
.btn-outline:hover { background: rgba(56, 189, 248, 0.1); }

#grid-wrapper {
    position: relative;
    margin: 20px 0;
}

#grid {
    display: grid;
    grid-template-columns: repeat(9, 1fr);
    gap: 1px;
    background: var(--cell-border);
    border: 3px solid var(--cell-border);
    border-radius: 12px;
    overflow: hidden;
}

#win-message, #about-overlay {
    position: absolute;
    top: 0; left: 0; right: 0; bottom: 0;
    background: rgba(15, 23, 42, 0.98);
    backdrop-filter: blur(15px);
    display: none;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    border-radius: 32px;
    z-index: 20;
    padding: 20px;
}

.about-content {
    text-align: left;
    width: 100%;
    max-width: 300px;
}
.about-item {
    display: flex;
    align-items: center;
    gap: 15px;
    margin: 15px 0;
    font-size: 0.9rem;
    color: var(--text);
}

/* 3. UPDATED ICON STYLING */
.about-item i {
    color: var(--accent);
    width: 20px;
    text-align: center;
    font-size: 1.1rem;
}

.about-item a {
    color: var(--text);
    text-decoration: none;
    transition: color 0.2s;
    word-break: break-all;
}
.about-item a:hover {
    color: var(--accent);
}

.cell {
    font-family: var(--font-display);
    aspect-ratio: 1;
    background: var(--cell-bg);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.4rem;
    font-weight: 400;
    cursor: pointer;
    transition: all 0.2s;
    color: var(--text);
}

.cell:nth-child(3n) { border-right: 2px solid var(--cell-border); }
.cell:nth-child(9n) { border-right: none; }
.cell:nth-child(n+19):nth-child(-n+27),
.cell:nth-child(n+46):nth-child(-n+54) { border-bottom: 2px solid var(--cell-border); }

.cell.selected { 
    background: #334155; 
    box-shadow: inset 0 0 10px var(--accent);
    color: var(--accent);
}

.cell.fixed { color: #64748b; font-weight: 700; background: rgba(0,0,0,0.2); cursor: default; }
.cell.hinted { color: var(--hint); text-shadow: 0 0 5px var(--hint); }

.numpad {
    display: grid;
    grid-template-columns: repeat(5, 1fr);
    gap: 8px;
}

.num-btn {
    font-family: var(--font-display);
    background: #1e293b;
    border: 1px solid var(--cell-border);
    color: white;
    padding: 12px;
    border-radius: 10px;
    cursor: pointer;
    font-weight: 700;
    font-size: 1.1rem;
}

.num-btn:hover:not(:disabled) { background: var(--cell-border); color: var(--accent); }

.hint-btn {
    grid-column: span 5;
    background: rgba(16, 185, 129, 0.1);
    color: var(--hint);
    border: 1px solid var(--hint);
    margin-top: 10px;
    font-size: 0.8rem;
}

.hidden { display: none !important; }

@keyframes pulse {
    0% { opacity: 1; }
    50% { opacity: 0.6; }
    100% { opacity: 1; }
}