estilo.css

.calculadora{
	display:block;
	margin:0 auto;
	padding: 20px;
	background-color: #DC4C46;
	width:350px;
	height:500px;
	border-radius: 25px;
}

.calculadora td button{
	display:block;
	width:70px;
	height: 70px;
	font-size:25px;
}

#resultado{
	display:block;
	text-align:center;
	font-size:40px;
	margin-bottom: 50px;
	width: 300px;
	height: 100px;
	line-height: 100px;
	background-color: #fff;
	border-radius: 25px;
	overflow-y: scroll;
}