In pages such as the one referenced, having Data Type:center causes the value to disappear. The end of the description for that value contains "</div>" and the rest of the content after that point renders as centered. 

The source:

{{CSS Property Value
|Data Type=center
|Description=Flexbox items are packed toward the center of the line. All child elements are placed edge to edge with each other, as described in the descriptions for the [#start start] or [#end end] keywords. However, the group of child elements is centered between the starting and ending edges of the parent element so that all remaining space is evenly distributed before the first child element and after the last child element.
}}{{CSS Property Value

            </div> gets rendered here in the page
...Everything after this is centered


|Data Type=justify
|Description=Flexbox items are evenly distributed in the line. The starting edge of the first child element is placed at the start of the parent element; the ending edge of the last child element is placed edge to edge with the end of the parent box; and all remaining children are placed between the first and last child elements, so that any space that remains along the layout axis is equally distributed between child elements.
}}

...