HTML and CSS Reference
In-Depth Information
While outlines may resemble borders, they take up no additional space and may overlay
other content outside of a block if need be, as shown here:
Because outlines are drawn over an item, rather than around it, they cause no reflow
when applied dynamically:
Hover Outline
Hover Border
Also note that outlines can appear as nonrectangular depending on how they are drawn
around items:
