CSS Margin Collapse

Last Updated : 02 Jul, 2021

The CSS margin property is used to set a margin on all four sides of an element.
When two elements are next to each other on a page vertically, one of the elements might lose its vertical margin. This means the top and bottom margins of elements are sometimes combined into a single margin. The single margin is equal to the largest of the two margins getting collapsed.
Example:

html

<!DOCTYPE html>
<!DOCTYPE html>
<html lang="en" dir="ltr">
    <head>
       <style>
           p{
               margin: 20px 0 10px;
               background-color:rgb(79, 236, 119);
           }
       </style>
    </head>
    <body>
         
<p>This paragraph's bottom margin is collapsed.</p>
 
         
<p>This paragraph is 20px below the above text.</p>
 
    </body>
</html>

You would expect the margin between the two paragraphs to be 30px (10px bottom margin of 1st paragraph + 20px top margin of next paragraph). But in CSS the bigger margin overrides and the actual margin is the bigger one (20px).
Output:

If one element has a negative margin, the negative margin is subtracted from the positive margin. For example, resultant margin of 40px and -30px will be 10px (40px-30px). If both the margins are negative, greater negative value is used. For example, resultant margin of -20px and -50px will be -50px.
The margins of floating and absolutely positioned elements never collapse.
Some specific cases of margins collapse:

Between adjacent elements:
The margins of vertically adjacent elements collapse as we saw in the previous example.
Between parent and child elements:
Adjacent margins of parent and child elements collapse when no padding, borders, or content exist between the adjacent margins.

Example:

html

<!DOCTYPE html>
<html lang="en" dir="ltr">
    <head>
       <style>
           h1{
              margin: 0;
              background-color: rgb(79, 236, 119);
           }
 
           div{
               margin: 30px 0 20px ;
           }
 
           p{
               margin: 20px 0 10px;
               background-color: #f0f0f0;
           }
       </style>
    </head>
    <body>
        <h1>Geeks For Geeks</h1>
        <div>
             
<p>This paragraph's top 
              margin is collapsed.</p>
 
        </div>
    </body>
</html>