@jfml It's because of the difference between elements that use the `block` and `inline` boxes. https://developer.mozilla.org/en-US/docs/Web/CSS/display

`text-align: center;` means it centres the content of elements with an inline type - the text *inside* the p, for example. Not the p itself.

When you want to centre "an HTML element" you likely want to centre *the element* and not *its content*. Which means it needs to be block level, and then you can use margins.