Jordan Moore (who has a name like a country singer:)
Say for example we want to present an article in the narrow single column view, but before the article appears in the stacking order we have: a header (containing site name etc), navigation, maybe even a banner advertisement, then the article. The heart of the page is buried beneath items that may be less important in this context. Rather than brutally hiding these items with a display:none property we can reorder them using another CSS property - flex box.
It takes something to make me sign in and blog on a Sunday, but this is good. Very good. Read the whole thing. Then study Jordan’s demo page. Brilliant.