Item with margin-top has margin outside of containing box

问题

I have something to this effect:

#div {
   background: green; 
   width: 200px;
   height: 100px;
}

h1 {
   margin-top: 100px;
}

(And obviously there is some HTML to go with it.)

Now when viewed in the browser the h1 shows at the very top of the #div and the 100px margin goes on top of the #div.

Can anyone suggest a reason?

(The code is a little too complicated to insert the relevant parts so if no-one can give me an answer then I will post it and maybe someone will spot an error or something.)

回答1:

Try to add padding instead. I've seen this kind of problem before. If the padding does the the same thing then try putting a container div around but #div and the h1 then add the margin. If you are just wanting to move the h1 down from the #div then padding is your best bet since it will "Push the h1 further into the #div 'box'".

回答2:

This is not related to the H1 tag. This is what we call margin collapse.

You can find a post about this subject here : http://reference.sitepoint.com/css/collapsingmargins

you have several solutions :

• use padding instead
• add overflow: auto on your parent div
• add transparent top border to the parent div

回答3:

I was able to solve this problem by making all of my header tags (h1-h6) display: inline-block;. As inline elements with margins, they can overflow like that, but as inline blocks they behave a little more nicely with others.

来源：https://stackoverflow.com/questions/6929874/item-with-margin-top-has-margin-outside-of-containing-box