The promoted links on the DUNE at Work site have been changed in size, color and placement. This goverened by a CSS text file in the Site Assets library.
The promoted link area on the page is governed by a section in the file. If you add an additional promoted link, you will need to increase the size of this area. This is what allows the links to be centered. There is a comment in the file that says you need to change the following when adding more promoted links. It looks like -
/* change the following if add more promoted links, needs to be slightly larger than (width below)*(number of links) */width:790px;display:inline-block; text-align:center;}
It is the 790px that needs to be changed.