WordPress: one page’s content is not centered, other pages all look the same [closed]

To center the main container, add:

body.page-id-16 .hentry-wrapper {
  margin-left: auto;
  margin-right: auto;
}

However, this looks like it pushes the content to the right. This is because the parent element is a lot wider than the viewport. Thus we should limit this element to the viewport width to actually center the content. We can add this:

body.page-id-16 .hentry {
  width: 100%;
}

The body.page-id-16 prefixes to the CSS selectors are to limit these CSS declarations to this exact page. This reduces any styling regressions to other pages that could otherwise be caused by these declarations being applied more globally.