.app{text-align:center;font-family:Arial,sans-serif}.instructions{color:#333;max-width:600px;margin:0 auto 20px;font-size:16px;line-height:1.5}.grid{grid-template-columns:repeat(9,40px);justify-content:center;margin:20px 0;display:grid}.cell{text-align:center;border:1px solid #555;width:40px;height:40px;font-size:18px}.border-right{border-right:3px solid #000}.border-bottom{border-bottom:3px solid #000}.fixed{background-color:#e0e0e0;font-weight:700}.buttons button{margin:10px;padding:10px 20px;font-size:16px}