.display-4 {
	font-size: 3rem; 
}
.calc {
	padding: 20px;
	margin: 20px 0;
	border: 1px solid #ccc;
	border-radius: 5px;
}
.calc input[type="number"]{
	text-align: right;
}
.calc input#result {
	background-color: white;
	border-radius: 0;
	border: none;
	border-bottom: 1px solid #ced4da; 
	text-align: right;
}
.calc input.invalid {
	border: 1px solid red;
}
.calc .display-table {
	margin: 0 auto;
}
.calc .display-cell {
	padding: 10px;
}
.calc .display-row.title .display-cell {
	background-color: #f1f1f1;
	border-top-left-radius: 5px;
}
.calc .display-row.title .display-cell:last-child {
	border-top-left-radius: 0;
	border-top-right-radius: 5px;
}
.calc button {
	min-width: 110px;
	margin: 0 10px 0 0;
}
.calc button:last-child {
	margin-right: 0;
}
.calc #messages li {
	color: red;
    list-style-type: square;	
}
.calc .plus-button {
    background-color: #838383;
    border-radius: 50%;
    display: inline-block;
    height: 25px;
    width: 25px;
    text-align: center;
    font-size: 20px;
    line-height: 20px;
    color: white;
    font-weight: bold;
    margin: 0 5px 0 0;
	cursor: pointer;
}
@media only screen and (max-width : 767px) {
	.content-wrapper h1	{
		margin-bottom: 50px;
	}
	.calc .display-cell {
		display: block;
	}
	.calc .display-cell.empty {
		display: none;
	}
	.calc .display-row.title .display-cell {
		border-top-right-radius: 5px;	
	}
}