In theory, you could just change the page content to using paragraphs, and it will work inline with the previous suggested code, else why not just apply the centering to the elements when writing the page.
ie.
<div style="text-align:center"></div>
Or create a class and give the elements you want to center that class.
ie.
.center { text-align:center; }
<div class="center"></div>
Or we could just forget all that and just try to center everything inside the post/page.
.post-content { text-align:center }
.post-content * { text-align:center }