Css – Setting width/height as percentage minus pixels

cssheightpixel

I'm trying to create some re-usable CSS classes for more consistency and less clutter on my site, and I'm stuck on trying to standardize one thing I use frequently.

I have a container <div> that I don't want to set the height for (because it will vary depending on where on the site it is), and inside it is a header <div>, and then an unordered list of items, all with CSS applied to them.

It looks a lot like this:

Widget

I want the unordered list to take up the remaining room in the container <div>, knowing that the header <div> is 18px tall. I just don't know how to specify the list's height as "the result of 100% minus 18px".

I've seen this question asked in a couple other contexts on SO, but I thought it would be worth asking again for my particular case. Does anyone have any advice in this situation?

Best Answer

You can use calc:

height: calc(100% - 18px);

Note that some old browsers don't support the CSS3 calc() function, so implementing the vendor-specific versions of the function may be required:

/* Firefox */
height: -moz-calc(100% - 18px);
/* WebKit */
height: -webkit-calc(100% - 18px);
/* Opera */
height: -o-calc(100% - 18px);
/* Standard */
height: calc(100% - 18px);

2015 update: the flexbox approach

There are two other answers briefly mentioning flexbox; however, that was more than two years ago, and they don't provide any examples. The specification for flexbox has definitely settled now.

Note: Though CSS Flexible Boxes Layout specification is at the Candidate Recommendation stage, not all browsers have implemented it. WebKit implementation must be prefixed with -webkit-; Internet Explorer implements an old version of the spec, prefixed with -ms-; Opera 12.10 implements the latest version of the spec, unprefixed. See the compatibility table on each property for an up-to-date compatibility status.

(taken from https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Flexible_boxes)

All major browsers and IE11+ support Flexbox. For IE 10 or older, you can use the FlexieJS shim.

To check current support you can also see here: http://caniuse.com/#feat=flexbox

Working example

With flexbox you can easily switch between any of your rows or columns either having fixed dimensions, content-sized dimensions or remaining-space dimensions. In my example I have set the header to snap to its content (as per the OPs question), I've added a footer to show how to add a fixed-height region and then set the content area to fill up the remaining space.

html,
body {
  height: 100%;
  margin: 0;
}

.box {
  display: flex;
  flex-flow: column;
  height: 100%;
}

.box .row {
  border: 1px dotted grey;
}

.box .row.header {
  flex: 0 1 auto;
  /* The above is shorthand for:
  flex-grow: 0,
  flex-shrink: 1,
  flex-basis: auto
  */
}

.box .row.content {
  flex: 1 1 auto;
}

.box .row.footer {
  flex: 0 1 40px;
}

<!-- Obviously, you could use HTML5 tags like `header`, `footer` and `section` -->

<div class="box">
  <div class="row header">
    <p><b>header</b>
      <br />
      <br />(sized to content)</p>
  </div>
  <div class="row content">
    <p>
      <b>content</b>
      (fills remaining space)
    </p>
  </div>
  <div class="row footer">
    <p><b>footer</b> (fixed height)</p>
  </div>
</div>

In the CSS above, the flex property shorthands the flex-grow, flex-shrink, and flex-basis properties to establish the flexibility of the flex items. Mozilla has a good introduction to the flexible boxes model.

Html – Div width 100% minus fixed amount of pixels

New way I've just stumbled upon: css calc():

.calculated-width {
    width: -webkit-calc(100% - 100px);
    width:    -moz-calc(100% - 100px);
    width:         calc(100% - 100px);
}

Source: css width 100% minus 100px

Best Answer

Related Solutions

Html – Make a div fill the height of the remaining screen space

2015 update: the flexbox approach

Working example

Html – Div width 100% minus fixed amount of pixels

Related Topic