Perfectly centerd cross-mark

HTML

<div class="plus"></div>
<div class="moins"></div>

CSS

html {
    background-color:#000;
}
	.plus{
		position: fixed;
		bottom: 20px;
		left: 5px;
		display:block;
		 background-color: rgba(204, 0, 102, 0);
		border: 2px solid #FFF;
		height: 31px;
		width: 32px;
		-moz-border-radius:75px;
		-webkit-border-radius: 75px;
	}
	.plus:after {
		position: absolute;
		top: 0;
		bottom: 0;
		left: 0;
		right: 0;
		content: "+";
		font-size: 32px; 
		color: #FFF;
		line-height: 1;
		text-align: center;   
	}
	.moins
	{
		position: fixed;
		bottom: 20px;
		right: 5px;
		display:block;
		 background-color: rgba(204, 0, 102, 0);
		border: 2px solid #FFF;
		height: 32px;
		width: 32px;
		-moz-border-radius:75px;
		-webkit-border-radius: 75px;
	}
	.moins:after {
		position: absolute;
		top: 0;
		bottom: 0;
		left: 0;
		right: 0;
		content: "-";
		font-size: 32px; 
		color: #FFF;
		line-height: 1;
		text-align: center;   
	}