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CSS CSS Layout Basics Getting Started with CSS Layout Why Vertical Margins Collapse

Why adding padding to only .main-header fixes collapse?

I tried adding padding: 1em 0; to .wrapper which contains .main-header, but it doesn't fix the collapse. I also tried adding the same padding statement to h1 tag but it doesn't fix it either.

Why does padding fix only works with .main-header class?

ywang04
ywang04
6,762 Points

As you said, .wrapper is the parent of .main-header. But the collapse doesn't occur between .wrapper and .main-header. You can set a border property to both of them to make sure there is no collapse between them. The collapse actually happens between h1 and .main-header while .main-header is the parent of h1.

@ywang04 thanks for reminding me to turn on borders to see where the collapse is happening.

1 Answer

Steven Parker
Steven Parker
229,982 Points

There's 3 types of margin collapse: sibling, parent-child, and empty element. Padding only stops the collapse if applied to the parent in parent-child collapse, or to an empty element. It no effect on sibling collapse or when applied to the child in a parent-child collapse. For more info see Mastering margin collapsing.

One other remedy I've always found odd is setting the overflow property on one of the elements in the collapse.

For some reason I thought since .wrapper is the parent of .main-header, it would also fix the collapse. Thanks.