Make div (height) occupy parent remaining height

Question

Expanding the #down child to fill the remaining space of #container can be accomplished in various ways depending on the browser support you wish to achieve and whether or not #up has a defined height.

Samples

.container {
  width: 100px;
  height: 300px;
  border: 1px solid red;
  float: left;
}
.up {
  background: green;
}
.down {
  background: pink;
}
.grid.container {
  display: grid;
  grid-template-rows: 100px;
}
.flexbox.container {
  display: flex;
  flex-direction: column;
}
.flexbox.container .down {
  flex-grow: 1;
}
.calc .up {
  height: 100px;
}
.calc .down {
  height: calc(100% - 100px);
}
.overflow.container {
  overflow: hidden;
}
.overflow .down {
  height: 100%;
}

<div class="grid container">
  <div class="up">grid
    <br />grid
    <br />grid
    <br />
  </div>
  <div class="down">grid
    <br />grid
    <br />grid
    <br />
  </div>
</div>
<div class="flexbox container">
  <div class="up">flexbox
    <br />flexbox
    <br />flexbox
    <br />
  </div>
  <div class="down">flexbox
    <br />flexbox
    <br />flexbox
    <br />
  </div>
</div>
<div class="calc container">
  <div class="up">calc
    <br />calc
    <br />calc
    <br />
  </div>
  <div class="down">calc
    <br />calc
    <br />calc
    <br />
  </div>
</div>
<div class="overflow container">
  <div class="up">overflow
    <br />overflow
    <br />overflow
    <br />
  </div>
  <div class="down">overflow
    <br />overflow
    <br />overflow
    <br />
  </div>
</div>

Grid

CSS's grid layout offers yet another option, though it may not be as straightforward as the Flexbox model. However, it only requires styling the container element:

.container { display: grid; grid-template-rows: 100px }

The grid-template-rows defines the first row as a fixed 100px height, and the remain rows will automatically stretch to fill the remaining space.

I'm pretty sure IE11 requires -ms- prefixes, so make sure to validate the functionality in the browsers you wish to support.

Flexbox

CSS3's Flexible Box Layout Module (flexbox) is now well-supported and can be very easy to implement. Because it is flexible, it even works when #up does not have a defined height.

#container { display: flex; flex-direction: column; }
#down { flex-grow: 1; }

It's important to note that IE10 & IE11 support for some flexbox properties can be buggy, and IE9 or below has no support at all.

Calculated Height

Another easy solution is to use the CSS3 calc functional unit, as Alvaro points out in his answer, but it requires the height of the first child to be a known value:

#up { height: 100px; }
#down { height: calc( 100% - 100px ); }

It is pretty widely supported, with the only notable exceptions being <= IE8 or Safari 5 (no support) and IE9 (partial support). Some other issues include using calc in conjunction with transform or box-shadow, so be sure to test in multiple browsers if that is of concern to you.

Other Alternatives

If older support is needed, you could add height:100%; to #down will make the pink div full height, with one caveat. It will cause overflow for the container, because #up is pushing it down.

Therefore, you could add overflow: hidden; to the container to fix that.

Alternatively, if the height of #up is fixed, you could position it absolutely within the container, and add a padding-top to #down.

And, yet another option would be to use a table display:

#container { width: 300px; height: 300px; border: 1px solid red; display: table;}
#up { background: green; display: table-row; height: 0; }
#down { background: pink; display: table-row;}​

Its been almost two years since I asked this question. I just came up with css calc() that resolves this issue I had and thought it would be nice to add it in case someone has the same problem. (By the way I ended up using position absolute).

http://jsfiddle.net/S8g4E/955/

Here is the css

#up { height:80px;}
#down {
    height: calc(100% - 80px);//The upper div needs to have a fixed height, 80px in this case.
}

And more information about it here: http://css-tricks.com/a-couple-of-use-cases-for-calc/

Browser support: http://caniuse.com/#feat=calc

Abstract

I didn't find a fully satisfying answer so I had to find it out myself.

My requirements:

• the element should take exactly the remaining space either when its content size is smaller or bigger than the remaining space size (in the second case scrollbar should be shown);
• the solution should work when the parent height is computed, and not specified;
• calc() should not be used as the remaining element shouldn't know anything about another element sizes;
• modern and familar layout technique such as flexboxes should be used.

---

The solution

• Turn into flexboxes all direct parents with computed height (if any) and the next parent whose height is specified;
• Specify flex-grow: 1 to all direct parents with computed height (if any) and the element so they will take up all remaining space when the element content size is smaller;
• Specify flex-shrink: 0 to all flex items with fixed height so they won't become smaller when the element content size is bigger than the remaining space size;
• Specify overflow: hidden to all direct parents with computed height (if any) to disable scrolling and forbid displaying overflow content;
• Specify overflow: auto to the element to enable scrolling inside it.

---

JSFiddle (element has direct parents with computed height)

JSFiddle (simple case: no direct parents with computed height)

My answer uses only CSS, and it does not use overflow:hidden or display:table-row. It requires that the first child really does have a given height, but in your question you state that only the second child need have its height not specified, so I believe you should find this acceptable.

#container {
  width: 300px;
  height: 300px;
  border: 1px solid red;
}

#up {
  background: green;
  height: 63px;
  float: left;
  width: 100%
}

#down {
  background: pink;
  padding-top: 63px;
  height: 100%;
  box-sizing: border-box;
}

<div id="container">
  <div id="up">Text<br />Text<br />Text<br /></div>
  <div id="down">Text<br />Text<br />Text<br /></div>
</div>

check the demo - http://jsfiddle.net/S8g4E/6/

use css -

#container { width: 300px; height: 300px; border:1px solid red; display: table;}
#up { background: green; display: table-row; }
#down { background:pink; display: table-row;}