Question

I have a div inside of another div. #outer and #inner. #outer has curved borders and a white background. #inner has no curved borders and a green background. #inner extends beyond the curved borders of #outer. Is there anyway to stop this?

#outer {
  display: block;
  float: right;
  margin: 0;
  width: 200px;
  background-color: white;
  overflow: hidden;
  -moz-border-radius: 10px;
  -khtml-border-radius: 10px;
  -webkit-border-radius: 10px;
  border-radius: 10px;
}

#inner {
  background-color: #209400;
  height: 10px;
  border-top: none;
}

<div id="outer">
  <div id="inner"></div>
  <!-- other stuff needs a white background -->
  <!-- bottom corners needs a white background -->
</div>

No matter how I try it still overlaps. How can I make #inner obey and fill to #outer‘s borders?

edit

The following hack served the purpose for now. But the question stands (maybe to the CSS3 and webbrowser writers): Why don’t child elements obey their parent’s curved borders and is there anyway to force them to?

The hack to get around this for my needs for now, you can assign curves to individual borders. So for my purposes, I just assigned a curve to the top two of the inner element.

#inner {
    border-top-right-radius: 10px; -moz-border-radius-topright: 10px; -webkit-border-top-right-radius: 10px;
    border-top-left-radius: 10px; -moz-border-radius-topleft: 10px; -webkit-border-top-left-radius: 10px;
}

Answer 1

According to the specs:

A box’s backgrounds, but not its
border-image, are clipped to the
appropriate curve (as determined by
‘background-clip’). Other effects that
clip to the border or padding edge
(such as ‘overflow’ other than
‘visible’) also must clip to the
curve. The content of replaced
elements is always trimmed to the
content edge curve. Also, the area
outside the curve of the border edge
does not accept mouse events on behalf
of the element.

http://www.w3.org/TR/css3-background/#the-border-radius

This means that an overflow: hidden on #outer should work. However, this won’t work for Firefox 3.6 and below. This is fixed in Firefox 4:

Rounded corners now clip content and images (if overflow: visible is not set).

https://developer.mozilla.org/en/CSS/-moz-border-radius

So you’ll still need the fix, just shorten it to:

#outer {
  overflow: hidden;
}

#inner {
  -moz-border-radius: 10px 10px 0 0;
}

See it working here: http://jsfiddle.net/VaTAZ/3/