*, ::before, ::after {
	box-sizing: border-box;
	margin: 0;
	padding: 0;
  }

body {
	font-family: Arial, sans-serif;
	text-align: center;
	background-color: #fff;
}
 
.calculator {
	margin: 50px auto;
	padding: 10px;
	border: 1px solid #ccc;
	width: 240px;
	background-color: #f7f7f7;
}
 
#display {
	width: 100%;
	height: 40px;
	font-size: 20px;
	text-align: right;
	margin-bottom: 10px;
}
 
button {
	width: 50px;
	height: 50px;
	font-size: 20px;
	margin: 5px;
	cursor: pointer;
}