:root {
    --bg: #18191a;
    --panel: #23272a;
    --cell: #282c34;
    --cell-border: #444950;
    --cell-border-strong: #6c63ff;
    --cell-highlight-try: #6c63ff;
    --cell-highlight-backtrack: #e53935;
    --text: #f1f1f1;
    --accent: #6c63ff;
    --button-bg: #6c63ff;
    --button-bg-hover: #5146d9;
}

body {
    background: var(--bg);
    color: var(--text);
    font-family: 'Segoe UI', Arial, sans-serif;
    margin: 0;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
}

h1 {
    color: var(--accent);
    letter-spacing: 2px;
    font-weight: 700;
    text-shadow: 0 2px 10px #000a;
    margin: 32px 0 24px 0;
    text-align: center;
}

#container {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
}

#panel {
    background: var(--panel);
    border-radius: 10px;
    padding: 18px 24px;
    margin-bottom: 18px;
    box-shadow: 0 4px 32px #0006;
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    justify-content: center;
    gap: 12px;
}

label, select, input[type="range"] {
    font-size: 16px;
    color: var(--text);
}

select, input[type="range"] {
    background: var(--panel);
    border: 1px solid var(--cell-border);
    border-radius: 4px;
    padding: 4px 8px;
}

button {
    padding: 8px 20px;
    background: var(--button-bg);
    color: #fff;
    border: none;
    border-radius: 5px;
    font-size: 16px;
    font-weight: 600;
    cursor: pointer;
    box-shadow: 0 2px 8px #0003;
    transition: background 0.2s, box-shadow 0.2s;
}

button:hover, button:focus {
    background: var(--button-bg-hover);
    box-shadow: 0 4px 16px #0004;
}

#speedValue {
    font-size: 14px;
    margin-left: 8px;
    color: var(--accent);
}

#sudoku-board {
    margin: 0 auto;
    display: inline-block;
    background: var(--panel);
    border-radius: 10px;
    box-shadow: 0 2px 24px #0006;
    padding: 20px 20px 10px 20px;
}

.sudoku-row {
    display: flex;
}

.sudoku-cell {
    width: 44px;
    height: 44px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 20px;
    background: var(--cell);
    color: var(--text);
    box-sizing: border-box;
    border: 1px solid var(--cell-border);
    transition: background 0.2s, border 0.2s;
}

.sudoku-cell.highlight-try {
    background: var(--cell-highlight-try) !important;
    border: 2px solid #fff !important;
    animation: pulse-try 0.2s;
}

.sudoku-cell.highlight-backtrack {
    background: var(--cell-highlight-backtrack) !important;
    border: 2px solid #fff !important;
    animation: pulse-back 0.2s;
}

@keyframes pulse-try {
    0% { box-shadow: 0 0 0 0 #6c63ff44; }
    100% { box-shadow: 0 0 8px 4px #6c63ff33; }
}

@keyframes pulse-back {
    0% { box-shadow: 0 0 0 0 #e5393544; }
    100% { box-shadow: 0 0 8px 4px #e5393533; }
}

#visual-status {
    margin-top: 18px;
    font-size: 18px;
    color: var(--accent);
    min-height: 24px;
    text-align: center;
}

@media (max-width: 600px) {
    #panel, #sudoku-board {
        padding: 10px;
    }
    .sudoku-cell {
        width: 30px;
        height: 30px;
        font-size: 14px;
    }
}