Help with theme CSS for centering image

When inserting images in a post the left and right images are fine but something is not right when I try to center an image.
In the editor, it looks fine but when the post goes live, the image is on the left.
I can’t figure out the CSS because it does not look to me like it is all categorized like on other themes I’ve had.

My site is http://www.lasvegasworldnews.com and here is the CSS

/*aligns*/
.aligncenter{ display:block;  margin: 0 auto}
.alignright{ float:right;  margin: 10px 0 10px 20px}
.alignleft{ float:left;  margin: 10px 20px 10px 0}

/*floats*/
.floatleft{ float:left}
.floatright{ float:right}

/*text style*/
.textcenter{ text-align:center}
.textright{ text-align:right}
.textleft{ text-align:left}

/*captions*/
.wp-caption{
	border:1px solid #ddd;
	text-align:center;
	background-color:#f3f3f3;
	padding-top:4px;
	margin:3px;
	-moz-border-radius:3px;
	-khtml-border-radius:3px;
	-webkit-border-radius:3px;
	border-radius:3px;
}
.wp-caption img{
	margin:0;
	padding:0;
	border:0 none;
}
.wp-caption p.wp-caption-text{
	font-size:11px;
	line-height:17px;
	padding:0 4px 5px;
	margin:0;
}

Can someone tell me what I need to add?

Much appreciated.