It will be unwise to plan such an effect with a Lightbox, as you will want better precision with locating the arrow in the middle of the text, plus a Lightbox can be a bit slow.
If I were to build this, I would approach the text and container as two children of the same parent occupying a single grid, and just hide/show or change the scale with a hover interaction.
As for the shape, in editor X it’s just two small containers added on top of the bigger one. One would be rotated, and the other will serve to hide the extra border, giving an illusion of a triangle.