This feature is obsolete. Although it may still work in some browsers, its use is discouraged since it could be removed at any time. Try to avoid using it.
Obsolete CSS features
display-insideCSS property specifies the inner display type of the box generated by an element, dictating how its contents lay out inside the box.
display-outsideCSS property specifies the outer display type of the box generated by an element, dictating how the element participates in its parent formatting context.