
When Does Margin Collapse Happen?
<p> Margin collapse typically occurs in three main situations:- Between parent and first/last child elements
- Between adjacent siblings
- On empty elements (where top and bottom margins have nothing separating them)
Adjacent Sibling Elements
<p> This is probably the most common case you'll run into. Imagine two paragraphs sitting one after another:<p>First paragraph</p> <p>Second paragraph</p><p> If both have a
margin-bottom
and margin-top
, their margins won't just add up — they'll collapse into a single margin equal to the larger of the two.<p> For example:- First
<p>
hasmargin-bottom: 20px
- Second
<p>
hasmargin-top: 30px
Parent and Child Margins
<p> Another tricky case is when a child element's margin touches the top or bottom edge of its parent. If the parent has no padding, border, or content to separate itself from the child's margin, the margins will collapse.<p> For example:<div class="parent"> <p>Child paragraph with margin-top: 20px</p> </div><p> If the
doesn't have a border, padding, or any other content before the <p>
, then that 20px top margin on the <p>
will actually push the whole parent down — as if the parent itself had that margin.<p> To stop this from happening, you can:
- Add
padding-top
to the parent
- Use a border like
border: 1px solid transparent
- Apply
overflow: hidden
on the parent
<p> These tricks create a “barrier” that prevents the margins from touching and collapse.
It Doesn't Happen Everywhere
<p> There are several cases where margin collapse won't happen. For example:
- If either element has a non-auto
display
value like flex
, grid
, or inline-block
- If there's a border, padding, or background between the margins
- If one of the elements is floated or absolutely positioned
<p> Also, remember again — horizontal margins never collapse , so you won't see this behavior with left or right margins.
<p> So yeah, margin collapse is just how CSS handles spacing by default in certain vertical scenarios. It's not a bug — it's intentional — but it can definitely trip you up if you're not aware of how it works.
<p> Basically that's it.
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