body {
    font-family: 'Poppins', sans-serif;
    background: #ffffff;
    margin: 0;
    padding: 0;
    color: #000000;
    overflow-x: hidden;
}

#game-container {
    width: 90%;
    max-width: 400px;
    margin: 2rem auto;
    padding: 2rem;
    background: #ffffff;
    border: 2px solid #000000;
    border-radius: 20px;
    box-shadow: 5px 5px 0px #000000;
    text-align: center;
}

#sudoku-board {
    display: grid;
    grid-template-columns: repeat(9, 1fr);
    grid-template-rows: repeat(9, 1fr);
    border: 2px solid #000;
    width: 100%;
    max-width: 360px;
    height: 360px;
    margin: 0 auto 2rem auto;
    gap: 0;
    background: #fff;
    padding: 2px;
}

.cell {
    border: 1px solid #ccc;
    text-align: center;
    font-size: 1.2rem;
    width: 40px;
    height: 40px;
    box-sizing: border-box;
    caret-color: #ff6b6b;
    transition: all 0.2s;
    display: flex;
    align-items: center;
    justify-content: center;
    background: #ffffff;
    cursor: pointer;
    outline: none;
}

.cell:nth-child(3n) {
    border-right: 3px solid #000;
}

.cell:nth-child(9n) {
    border-right: none;
}

.row:nth-child(3n) .cell {
    border-bottom: 3px solid #000;
}

.row:nth-child(9) .cell {
    border-bottom: none;
}

.cell.fixed {
    background-color: #f0f0f0;
    font-weight: 600;
}

.cell.selected {
    background-color: #feca57;
}

.cell.highlight {
    background-color: #ff6b6b40;
}

.cell.incorrect {
    background-color: #ff000020;
    border-color: #ff0000;
}

#controls {
    text-align: center;
    margin-top: 2rem;
}

#controls button {
    background: linear-gradient(45deg, #ff6b6b, #feca57);
    color: white;
    border: none;
    border-radius: 10px;
    padding: 0.75rem 1.5rem;
    font-weight: 600;
    cursor: pointer;
    box-shadow: 3px 3px 0px #000000;
    transition: transform 0.2s, box-shadow 0.2s;
    margin: 0.5rem;
}

#controls button:hover {
    transform: translateY(-3px);
    box-shadow: 6px 6px 0px #000000;
}

#difficulty {
    margin-bottom: 1rem;
}

#difficulty span {
    font-weight: 600;
    margin-right: 1rem;
}

#difficulty button {
    background: #ffffff;
    color: #000000;
    border: 2px solid #000000;
    padding: 0.5rem 1rem;
    font-size: 0.9rem;
}

#difficulty button.active {
    background: #000000;
    color: #ffffff;
}

.back-button {
    position: absolute;
    top: 2rem;
    left: 2rem;
    text-decoration: none;
    color: #000000;
    font-weight: 600;
}