.oi-blank::before,
.oi-sigma::before
{
	display: inline-block;
	width: 1em;
	position: relative;
	
	top: 0.5em;
	left: 0.5em;
	transform: translate(-50%,-50%);
	padding: 0px;
	margin: 0px;	
}

.oi-blank::before
{
    content: ' ';
}

.oi-sigma::before
{
    content: '\2211';
}