The background extends to the outside edge of the border (but underneath the border in z-ordering).
The background extends to the outside edge of the border (but underneath the border in z-ordering).
MDN
The background is painted within (clipped to) the content box.
The background is painted within (clipped to) the content box.
MDN
No background is drawn below the border (background extends to the outside edge of the padding).
No background is drawn below the border (background extends to the outside edge of the padding).
MDN
The background-clip CSS property specifies whether an element's background, either the color or image, extends underneath its border.
If there is no background image, this property has only visual effect when the border has transparent regions (because of border-style) or partially opaque regions; otherwise the border covers up the difference.
MDN