Twenty Thirteen child theme styling – adjusting sidebar position

I found the css location via stylesheet line 2397:

.site-main .widget-area {
	-webkit-box-sizing: border-box;
	-moz-box-sizing:    border-box;
	-ms-box-sizing:     border-box;
	box-sizing:         border-box;
	float: right;
	width: 300px;
}

If I wanted to push the sidebar over o the right…. would I simply be able to add a definer here (on my child theme)?