If I go through and change the centering of the element in the different break point, do I have to change the webpage or would that be part of the CSS.
Rick, in general (seems it would apply to RLM too), you can set the positioning for various breakpoints within your CSS.
For example... If you have a logo in your header that's floated to the left at larger screen sizes, you could choose to remove the float and center it on small screens. You can do this for any page element...Four paragraphs side by side at full width, down to two over two at pad size and one centered column for phones.
That's why prototyping with something like RLM is good, it let's you easily try out layout configurations so by the time you've exported to the Editor, you have those breakpoints and CSS rules all figured out.