The outline-offset CSS property sets the amount of space between an outline and the edge or border of an element. An outline is a line that is drawn around an element, outside the border edge. The space between an element and its outline is transparent; in other words, it is the same as the parent element's background.
The width of the space between the element and its outline. A negative value places the outline inside the element. A value of 0 places the outline so that there is no space between it and the element.