>> You've been able to do exactly what you describe (i.e. putting "hello" squarely in the middle of a 600x600 yellow box) with CSS since its first incarnation, with e.g. the `valign` HTML attribute corresponding to the `vertical-align` CSS property on an `inline`, `inline-block` or `table-cell` box.

Notably not a `block` element like a div or p - which is what most people are going to use as a container.