CSS - Margin collision between 2 DIVs

Question

I have two DIV`s and i think I have a margin collision...

Example box


        
      

Answer 1

As others have already said, this is known as collapsing margins:

8 Box model - 8.3.1 Collapsing margins

In CSS, the adjoining margins of two or more boxes (which might or might not be siblings) can combine to form a single margin. Margins that combine this way are said to collapse, and the resulting combined margin is called a collapsed margin.

In this case, they are sibling elements; therefore the following applies:

Margins between a floated box and any other box do not collapse (not even between a float and its in-flow children).

Floating one of the sibling elements would prevent the margins from collapsing:

EXAMPLE HERE

These are NOT
collapsing

Margins of inline-block boxes do not collapse (not even with their in-flow children).

Making an element inline-block would also prevent the margins from collapsing:

EXAMPLE HERE

These are NOT
collapsing

---

Assuming the elements weren't siblings, you could add overflow:hidden to the parent element, as the following would then apply:

Margins of elements that establish new block formatting contexts (such as floats and elements with 'overflow' other than 'visible') do not collapse with their in-flow children.