Based on these two underlined alignment icons…
The left one is 'Align to horizontal center".
And since the horizon goes sideways, this should position the element in the center with equal space on the left and right, which it does.
But this icon suggests it’s VERTICAL alignment, does it not?
I think these two underlined icons need to be switched around.
I think the icons are intentionally this way - since the horizon lines remain the same direction and consistent through the grouped actions (e.g. align left, align to horizontal center, align to right).
Oh, I see it now, the box is being aligned relative to the dashes.
I was seeing the dashes as representing the space around the element, and I saw the equal dashes as equal spacing around the box.