Conflito de Margem CSS

Margin collapsing refers to the formation of a margin when two vertical margins meet.

The height of the merged margin is equal to the larger of the two margins that are collapsing.

Margin collapsing

Margin collapsing (stacking) is a relatively simple concept. However, in practice, it can cause a lot of confusion when laying out web pages.

In simple terms, margin collapsing refers to the formation of a margin when two vertical margins meet. The height of the merged margin is equal to the larger of the two margins that are collapsing.

When an element appears above another element, the bottom margin of the first element and the top margin of the second element will collapse. See the following diagram:

Exemplo de Conflito de Margem CSS 1

Try it yourself

When an element is contained within another element (assuming there are no padding or borders to separate the margins), their top and/or bottom margins will also collapse. See the following diagram:

Exemplo de Conflito de Margem CSS 2

Try it yourself

Although it may seem a bit strange, margins can even collapse with themselves.

Suppose there is an empty element with a margin but no border or padding. In this case, the top margin and the bottom margin will meet, and they will collapse:

Exemplo de Conflito de Margem CSS 3

If this margin encounters the margin of another element, it will also collapse:

Exemplo de Conflito de Margem CSS 4

This is why a series of paragraph elements occupies such a small space, because all their margins collapse into a small margin.

Margin collapsing may seem a bit strange at first glance, but in fact, it makes sense. Take a typical text page composed of several paragraphs as an example. The space above the first paragraph is equal to the paragraph's top margin. If there is no margin collapsing, the margins between all subsequent paragraphs will be the sum of the adjacent top and bottom margins. This means that the space between paragraphs will be twice the space at the top of the page. If margin collapsing occurs, the top and bottom margins between paragraphs will merge together, making the distances consistent throughout.

Significado Real do Conflito de Margem CSS

Note:Only the vertical margins of block boxes in the normal document flow will have margin collapsing. The margins between inline boxes, floating boxes, or absolutely positioned boxes will not collapse.

All CSS margin properties

Atributo Descrição
margin Propriedade abreviada usada para definir propriedades de margem em uma única declaração.
margin-bottom Definir a margem inferior externa do elemento.
margin-left Definir a margem esquerda externa do elemento.
margin-right Definir a margem direita externa do elemento.
margin-top Definir a margem superior externa do elemento.