* {
    box-sizing: border-box;
}

body {
    font-family: Arial, sans-serif;
    margin: 0;
    background: #f4f4f4;
    font-size: 16px;
}

.container {
    max-width: 420px;
    margin: 20px auto;
    background: white;
    padding: 20px;
    border-radius: 8px;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
}

.header {
    display: flex;
    justify-content: center;
    align-items: center;
    flex-wrap: wrap;
    gap: 12px;
    padding: 12px 16px;
    background: #333;
    color: white;
    margin-bottom: 10px;
}

.header a {
    color: #fff;
    background: #e74c3c;
    padding: 8px 14px;
    border-radius: 4px;
    text-decoration: none;
    font-weight: bold;
    font-size: 0.95rem;
}

.header a:hover {
    background: #c0392b;
}

.points {
    font-weight: bold;
    background: #444;
    padding: 8px 12px;
    border-radius: 4px;
}

.error { color: red; }
.success { color: green; }

label {
    display: block;
    margin: 12px 0;
}

input, button {
    width: 100%;
    padding: 12px;
    margin-top: 4px;
    font-size: 1rem;
    border: 1px solid #ccc;
    border-radius: 4px;
}

button {
    background: #333;
    color: white;
    border: none;
    cursor: pointer;
    margin-top: 10px;
}

button:hover {
    background: #555;
}

/* Sudoku Grid */
#sudoku-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 4px;
    margin: 20px auto;
    max-width: 320px;
    width: 100%;
}

#sudoku-grid input {
    width: 100%;
    aspect-ratio: 1;
    text-align: center;
    font-size: 1.4rem;
    font-weight: bold;
    padding: 0;
    border: 1px solid #999;
    border-radius: 4px;
}

#sudoku-grid input:focus {
    outline: 2px solid #3498db;
    border-color: #3498db;
}

/* Mobile adjustments */
@media (max-width: 480px) {
    .container {
        margin: 10px;
        padding: 15px;
    }

    .header {
        flex-direction: column;
        text-align: center;
        gap: 8px;
    }

    #sudoku-grid {
        max-width: 100%;
        gap: 3px;
    }

    #sudoku-grid input {
        font-size: 1.2rem;
    }

    h1, h2 {
        font-size: 1.4rem;
    }
}