box models | web.dev

.borderBox = content + padding + border (+ scrollbars, if present)

⭐️ Note: .offsetParent returns null in the following situations:

in the standard box model： size = content(width, height) + padding + border.
if box-sizing: box-sizing： size = (width, height)

.paddingBox = content + padding

position: (.clientTop, .clientLeft) in .borderBox

size: (.clientWidth, .clientHeight)

for inline elements and elements with no CSS(❓), they all return zero.