Understanding Outline vs Border in the Box Model
In the CSS box model, border and outline are both visible lines around an element, but they behave differently and serve distinct purposes.
Border: Part of the box model. It occupies space, contributing to the element's total width and height.
Outline: Drawn outside the element’s box. It does not occupy space and does not affect layout or element size.
Borders can have different styles on each side (
border-top,border-right, etc.), while outlines are uniform around the element.Outlines are often used for accessibility focus indicators, without affecting layout.
In this example, the border contributes to the total width and height of .box, while the outline is drawn outside the box and does not change its size. You can see the outline without it affecting layout.
Use borders when you want the line to be part of the element’s size and layout.
Use outlines for visual emphasis or accessibility focus indicators without altering layout.
box-sizingaffects borders but has no effect on outlines.Outlines can overlap other elements since they don’t occupy space.