In brief
outline-style selects the outline around an element. Unlike a border, the outline does not reserve space in the same way and can overlap nearby content.
Useful to know
outline-style selects the outline around an element. Unlike a border, the outline does not reserve space in the same way and can overlap nearby content. [1]
This suits focus indication without shifting neighbours. Still check tightly packed controls: an unchanged layout does not mean the outline cannot visually intersect another element.
Sources
For further detail and to check the information: