Margin-top doesn't work as intended

Question

Please look at the following example: https://jsfiddle.net/9wbm179c/

The margin-top:50px; is making this ugly gap between body and .outter . Just read the code and this message again: between body and .outter ... Isn't it should be making the gap between .inner and .outter ?

 html, body { padding: 0; margin: 0; } body { background: #777; } .outter { background: #099; text-align: center; } .inner { background: #ff0; width: 400px; height: 150px; margin: 0 auto; margin-top: 50px; } 

 <div class="outter"> <div class="inner"> </div> </div> 

Answer 1

What you're seeing is called "margin collapse." https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Box_Model/Mastering_margin_collapsing

Parent and first/last child - If there is no border, padding, inline content, block_formatting_context created or clearance to separate the margin-top of a block from the margin-top of its first child block, or no border, padding, inline content, height, min-height, or max-height to separate the margin-bottom of a block from the margin-bottom of its last child, then those margins collapse. The collapsed margin ends up outside the parent.

You can address it a number of ways. One way is by using overflow:hidden; on the parent element .outter . You could also use padding-top: 50px on .outter instead of margin-top on .inner

 html,body { padding:0; margin:0; } body { background:#777; } .outter { background:#099; text-align:center; overflow: hidden; } .inner { background:#ff0; width:400px; height:150px; margin:0 auto; margin-top:50px; } 

 <div class="outter"> <div class="inner"> </div> </div>