The content section is set to float left by default, and the sidebar is set to float right. The only way to bring them closer is to make the sidebar float left instead of right….or increase the width of the content or sidebar so they are closer together. Thats about the only way to do it since they both float and align to the opposite sides of each other.
I’d try setting the sidebar to float left and then either add padding-left to the sidebar to increase the space or padding-right to the content. You can find this code around line 720 –
/* ### Primary Sidebar */
.sidebar-primary {
float: right;
width: 340px;
}