.calculator {
	border: 2px solid #999;
	border-radius: 5px;
	padding: 10px;
	width: 300px;
	margin: 0 auto;
}
input[type="text"] {
	width: 100%;
	margin-bottom: 10px;
	font-size: 18px;
	padding: 5px;
	border-radius: 5px;
	border: none;
	background-color: #f3f3f3;
}
input[type="button"] {
	width: 50px;
	height: 50px;
	font-size: 18px;
	border-radius: 5px;
	margin-right: 5px;
	margin-bottom: 5px;
}