:root {
    --bg-color: #000000;
    --board-bg: #000000;
    --text-main: #ffffff;
    --text-muted: #888888;
    
    --primary: #ffffff;      /* Main border/text */
    --accent: #4ade80;       /* Green for success/active */
    --danger: #ff3333;       /* Red for errors */
    --highlight: #333333;    /* Selected cell */
    --related: #1a1a1a;      /* Row/Col highlighting */
    --same-num: #004400;     /* Same number highlighting */
    
    --border-thin: #333333;
    --border-thick: #ffffff;
    --border-btn: #666666;   /* Grey outline for buttons */
    
    --font-arcade: 'Press Start 2P', cursive;
}

body {
    background-color: var(--bg-color);
    color: var(--text-main);
    font-family: var(--font-arcade);
    margin: 0;
}

#sudoku-app {
    max-width: 800px;
    margin: 0 auto;
    padding: 20px;
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 30px;
}

/* --- Header & Stats --- */
.game-header {
    text-align: center;
    width: 100%;
    margin-bottom: 10px;
}

.game-title {
    font-size: 2rem;
    color: var(--text-main);
    text-transform: uppercase;
    margin-bottom: 20px;
    text-shadow: none;
    line-height: 1.5;
}

.game-stats {
    display: flex;
    justify-content: space-between;
    width: 100%;
    max-width: 500px;
    margin: 0 auto;
    font-size: 0.8rem;
    color: var(--text-muted);
    text-transform: uppercase;
}

.stat-item {
    background: transparent;
    padding: 5px;
}

/* --- Game Board --- */
.game-layout {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 30px;
    width: 100%;
}

.sudoku-board {
    display: grid;
    grid-template-columns: repeat(9, 1fr);
    width: 100%;
    max-width: 500px;
    aspect-ratio: 1;
    background: var(--board-bg);
    border: 4px solid var(--border-thick);
    user-select: none;
}

.cell {
    position: relative;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.2rem;
    color: var(--text-main);
    border-right: 1px solid var(--border-thin);
    border-bottom: 1px solid var(--border-thin);
    cursor: pointer;
}

/* Grid Lines */
.cell:nth-child(9n) { border-right: none; }
.cell.border-right-thick { border-right: 4px solid var(--border-thick); }
.cell.border-bottom-thick { border-bottom: 4px solid var(--border-thick); }

/* Cell States */
.cell.initial { color: var(--text-muted); }
.cell.user-input { color: var(--accent); }
.cell.error { color: var(--danger); }
.cell.selected { background-color: var(--highlight); }
.cell.related { background-color: var(--related); }
.cell.same-num { background-color: var(--same-num); }

/* Notes */
.notes-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    grid-template-rows: repeat(3, 1fr);
    width: 100%;
    height: 100%;
    pointer-events: none;
}
.note-num {
    font-size: 0.4rem;
    color: var(--text-muted);
    display: flex;
    align-items: center;
    justify-content: center;
}

/* --- Controls Section --- */
.controls-container {
    width: 100%;
    max-width: 500px;
    display: flex;
    flex-direction: column;
    gap: 15px;
}

/* Top Row: Actions */
.action-row {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
}

/* Bottom Grid: Numpad (2x5) */
.numpad-grid {
    display: grid;
    grid-template-columns: repeat(5, 1fr);
    gap: 10px;
}

/* Buttons */
button {
    font-family: var(--font-arcade);
    background: #000;
    border: 2px solid var(--border-btn); /* Changed to grey outline */
    color: var(--text-main);
    padding: 15px 5px;
    cursor: pointer;
    text-transform: uppercase;
    font-size: 0.7rem;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 5px;
    transition: all 0.1s;
}

button:hover {
    background: var(--highlight);
    border-color: var(--text-main);
}

button:active {
    background: var(--text-main);
    color: var(--bg-color);
    transform: translateY(2px);
}

button.active {
    background: var(--text-main);
    color: var(--bg-color);
    border-color: var(--text-main);
}

button.num-btn {
    font-size: 1.2rem;
    padding: 20px 0;
}

/* Modal */
.modal-overlay {
    position: fixed;
    top: 0; left: 0; right: 0; bottom: 0;
    background: rgba(0,0,0,0.85);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 2000;
    opacity: 0;
    pointer-events: none;
    transition: opacity 0.2s;
}
.modal-overlay.show {
    opacity: 1;
    pointer-events: auto;
}

.modal-content {
    background: #000;
    border: 4px solid var(--border-thick);
    padding: 40px;
    text-align: center;
    max-width: 500px;
    width: 90%;
}

.modal-title {
    font-size: 1.5rem;
    color: var(--accent);
    margin-bottom: 20px;
    text-transform: uppercase;
}

.modal-text {
    font-size: 0.8rem;
    margin-bottom: 30px;
    line-height: 1.8;
}

.modal-actions {
    display: flex;
    flex-direction: column;
    gap: 15px;
}

.modal-actions button {
    width: 100%;
    padding: 15px;
    font-size: 1rem;
    border-color: var(--border-thick); /* Modal buttons keep white border for emphasis */
}

.modal-row {
    display: flex;
    gap: 10px;
    justify-content: center;
}

/* Responsive adjustments */
@media (max-width: 600px) {
    .game-title { font-size: 1.5rem; }
    .cell { font-size: 1rem; }
    .numpad-grid { gap: 5px; }
    button.num-btn { padding: 15px 0; font-size: 1rem; }
    .action-row { gap: 5px; }
    button { padding: 10px 2px; font-size: 0.6rem; }
    .modal-content { padding: 20px; }
}