.cell input { 
	width: 3em; 
	height: 3em; 
	text-align: center; 
	font-size: large; 
	border: 1px solid lightblue;
}

.r { 
	border-right: 2px solid grey; 
}

.d { 
	border-bottom: 2px solid grey; 
}

#puzzle { 
	border-spacing:0; 
	border-collapse:collapse; 
	margin: 20px auto;
}

.center {
	margin: 0 auto;
}

.btn {
	width: 10em;
}

.btn-default:focus {
    background-color: #fff;
    border-color: #ccc;
}

.btn-default:hover {
    color: #333;
    background-color: #e6e6e6;
    border-color: #adadad;
}