body {
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    margin: 0;

    font-family: 'Segoe UI', Roboto, sans-serif;
}

.container {
    width: 100%;
    text-align: center;
}

.header {
    display: flex;
    justify-content: space-between;
    align-items: center;

    max-width: 90vw;
    margin: 0 auto;

    h1 {
        border-radius: 10px;
        padding: 5px 20px 10px;
        color: whitesmoke;
    }
}

.sudoku-grid {
    width: 90vw;
    height: 90vw;            /* sorgt für quadratische Gesamtfläche */
    max-width: 90vh;         /* nimmt die kleinere Dimension */
    max-height: 90vh;

    margin: 0 auto;

    display: grid;
    grid-template-columns: repeat(9, 1fr);
    grid-template-rows: repeat(9, 1fr);

    gap: 2px;

    .cell {
        width: 100%;
        height: 100%;

        text-align: center;
        font-size: 2rem;
        font-weight: bold;

        box-sizing: border-box;
        border: 1px solid #999;
    }

    .cell::placeholder {
        font-size: 10px;
    }

    .cell.highlight {
        background-color: lightgoldenrodyellow;
    }

    .cell.selected {
        background-color: lightsalmon;
    }

    .cell.invalid {
        background-color: #f44336;
        color: white;
    }

    .cell.found {
        color: #2e7d32
    }

    .cell.fork {
        color: #4CAF50;
    }

    .cell:nth-child(3n) {
        border-right: 2px solid black;
    }

    .cell:nth-child(9n+1) {
        border-left: 2px solid black;
    }

    .cell:nth-child(n+73):nth-child(-n+81) {
        border-bottom: 2px solid black;
    }

    .cell:nth-child(-n+9),
    .cell:nth-child(n+28):nth-child(-n+36),
    .cell:nth-child(n+55):nth-child(-n+63) {
        border-top: 2px solid black;
    }
}

.sudoku-grid.sudoku-solved {
    border: solid 10px #4CAF50;
}

.sudoku-grid.sudoku-unsolveable {
    border: solid 10px #f44336;
}

.buttons {
    margin-top: 25px;
    margin-bottom: 25px;
    display: flex;
    justify-content: center;
    gap: 15px;
}

.buttons button {
    padding: 10px 20px;
    font-size: 1rem;
    border: none;
    border-radius: 10px;
    cursor: pointer;
    
    color: whitesmoke;

    box-shadow: 0 4px 10px rgba(0,0,0,0.2);
    transition: all 0.2s ease;
}

/* Hover Effekt */
.buttons button:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 14px rgba(0,0,0,0.25);
}

/* Klick Effekt */
.buttons button:active {
    transform: translateY(0);
    box-shadow: 0 3px 8px rgba(0,0,0,0.2);
}

.start, .solved {
    background: linear-gradient(135deg, #4CAF50, #2e7d32);
}

.reset, .unsolveable {
    background: linear-gradient(135deg, #f44336, #c62828);
}

.title, .stop {
    background: linear-gradient(135deg, #2196f3, #1565c0);
}

.copyright {
    margin-bottom: 10px;
}