Setting a length (height or width) for one element minus the variable length of another, i.e. calc(x - y), where y is unknown


I know we can use calc when lengths are defined:

flex-basis: calc(33.33% - 60px);
left: calc(50% - 25px);
height: calc(100em/5);

But what if a length is variable?

height: calc(100% - <<header with variable height>>);

OR

width: calc(100% - 50px - <<box with variable width>>);

enter image description here

Is there a standard way to do this in CSS?

I know the overall task is possible with flexbox and tables, but I'm wondering if CSS offers a simpler method. Flexbox, tables and simple Javascript are acceptable alternatives.

height demo

width demo

You can use CSS tables:

.wrapper {
  display: table;
  width: 100%;
  margin: 15px 0;
}

.horizontal.wrapper > div {
  display: table-cell;
  white-space: nowrap; /* Prevent line wrapping */
  border: 1px solid;
}
.left { width: 100px } /* Minimum width of 100px */
.center { width: 0; }  /* Width given by contents */

.vertical.wrapper { height: 200px; }
.vertical.wrapper > div {
  display: table-row;
}
.vertical.wrapper > div > span {
  display: table-cell;
  border: 1px solid;
}
.top    { height: 100px; } /* Minimum heigth of 100px */
.middle { height: 0; }     /* Height given by content */
.bottom { height: 100%; }  /* As tall as possible */
<div class="horizontal wrapper">
  <div class="left">100px wide</div>
  <div class="center">Auto width, given by contents</div>
  <div class="right">Remaining space</div>
</div>
<div class="vertical wrapper">
  <div class="top"><span>100px tall</span></div>
  <div class="middle"><span>Auto height, given by contents</span></div>
  <div class="bottom"><span>Remaining space</span></div>
</div>

The horizontal case can also be achieved with floats:

#wrapper, .right { overflow: hidden; } /* Establish BFC */
#wrapper > div { border: 1px solid; }
.left, .middle { float: left; }
.left { width: 100px }
<div id="wrapper">
  <div class="left">100px</div>
  <div class="middle">Auto width, given by contents</div>
  <div class="right">Remaining space</div>
</div>


Flexbox can do that.

Support is IE10 and up.

JSfiddle Demo

* {
  margin: 0;
  padding: 0;
}
html,
body {
  height: 100%;
}
#container {
  height: 100%;
  display: flex;
  flex-direction: column;
}
#top {
  background-color: lightgreen;
}
#bottom {
  background-color: lightblue;
  flex: 1;
}
<div id="container">
  <div id="top">green box variable height</div>
  <div id="bottom">blue box no longer overflows browser window</div>
</div>


Updated

As I commented earlier, and besides flex, this is also solvable using display: table and here is a fiddle demo I made showing that.

If a fixed top also were required for the vertical demo, here is an update of my original display:table version: fiddle demo

Sometimes I haven't been able (or didn't want) to use either flex nor tables, and I have, on and off, looked into making use of css calc() and css attr().

Both come short though, as calc() can only use +-*/ and attr() can only return a string value, which can't be computed by calc().

My suggestion, using plain javascript, is based on that these 2 methods, at some point, might be extended so we can make better use of them.

This is how I would like see them work;

width: calc(100% - attr(this.style.left))

but as they don't, and I can't add it to my css either as it wouldn't validate properly (might even break the parsing, who knows) I added a variant as an attribute on the element instead, with some quirks to make it easier to compute.

And in this case (the 2 demos) it looks like this:

//height
<div id="bottom" data-calcattr="top,height,calc(100% - toppx)">...</div>

//width 
<div class="box right" data-calcattr="left,width,calc(100% - leftpx)">...</div>

Together with below script, which by no means is fully developed/tested on all property combinations, it does adjust the div's size.

In short, when runned, it take the attribute, split it into an array, take the first item value as from which property to read, the second to which property to set and the third to which the read value gets inserted/replaced and assigned to the property to be set (hmmm, still working on a better way to express this, but hopefully the script is clear enough with whats going on).

Here is a fiddle showing both the height and width demo, integrated, making use of the same script.

function calcattr() {
    var els = document.querySelectorAll('[data-calcattr]');
    for (i = 0; i < els.length; i++) {
        var what = els[i].getAttribute('data-calcattr');
        if (what) {
            what = what.split(',');
            var rect = els[i].getBoundingClientRect();
            var parentrect = els[i].parentNode.getBoundingClientRect();
            var brd = window.getComputedStyle(els[i].parentNode,null).getPropertyValue('border-' + what[0] + '-width');            
            what[2] = what[2].replace(what[0],parseInt(rect[what[0]]-parentrect[what[0]]) - parseInt(brd));
            els[i].setAttribute("style", what[1] + ":" + what[2]);
        }
    }
}

IN CSS

Although I've never tried it, I believe that this would work:

.top {
    height:13px;
}

.main {
    height:calc(100% - var(height));
}

http://www.creativebloq.com/netmag/why-you-need-use-css-variables-91412904


IN SASS

$top_height: 50px

.main {
    height: calc(100% - $top_height)
}

Sass Variable in CSS calc() function


In both cases on container css you should put:

#container {
    overflow: hidden;
}

But, it will hide the information that overflows the container. I think that is the point, since you put white-space: nowrap; it means that you don't want to change the height, so you have to hide the text that can't fits the container.


I'm looking for something simple and portable. In the same way a CSS property can be easily applied across documents, I'm looking for something similar in terms of ease-of-application for this function.

... isolated fix is preferred.

Horizontal:

This can be achieved using CSS only. As you do not prefer a flex layout solution, the next best bet would be a table layout.

A simple CSS snippet which you could drop into your project (and be done with) would look like this:

div.flexh {
    display: table; box-sizing: border-box; padding: 0; margin: 0;
}
div.flexh > div { 
    display: table-cell; width: auto; 
    box-sizing: border-box; vertical-align: middle;
}
div.flexh > div:first-child {
    /* Override your custom styling below */
    min-width: 75px; width: 75px; max-width: 75px; 
}
div.flexh > div:last-child { width: 100%; }

You can then add your site-specific styling to this base CSS as per site requirements. Like, nowrap etc.

Two apparent advantages of this solution are:

  1. You do not need to change your markup and also do not need to decorate all children with classes. Just apply the class flexh to your parent div and that would be it.

Minimal Markup Required:

<div class="flexh">
    <div>...</div>
    <div>...</div>
    <div>...</div>
</div>
  1. You are not limited to just three columns. You could have as many columns as need be. The first one will have fixed width, the last one will be flexible, and all the columns in-between would get content-based widths.

Demo Fiddle: http://jsfiddle.net/abhitalks/qqq4mq23/

Demo Snippet:

div.flexh {
    display: table; box-sizing: border-box; padding: 0; margin: 0;
    /* Override your custom styling below */
    width: 80%; border: 2px solid black;
    border-right: 2px dashed black; 
    font-size: 1em;
}
div.flexh > div { 
    display: table-cell; width: auto; 
    box-sizing: border-box; vertical-align: middle;
    /* Override your custom styling below */
    background-color: lightgreen; border: 1px solid #ddd;
    padding: 15px 5px;
}
div.flexh > div:first-child {
    /* Override your custom styling below */
    min-width: 75px; width: 75px; max-width: 75px; 
    background-color: orange;
}
div.flexh > div:last-child {
    width: 100%;
    /* Override your custom styling below */
    background: skyblue;
}
<div class="flexh">
    <div>75px Fixed Width</div>
    <div>Variable Content Width</div>
    <div>Flexible Remaining Width</div>
</div>

<hr/>
<div class="flexh">
    <div>75px Fixed Width</div>
    <div><img src='//placehold.it/128x48/66c' /></div>
    <div>Flexible Remaining Width</div>
</div>

<hr/>
<div class="flexh">
    <div>75px Fixed Width</div>
    <div>Variable TextWidth</div>
    <div>
        <img src='//placehold.it/128x48/66c' />
        <p>Variable ContentWidth</p>
    </div>
    <div>Flexible Remaining Width</div>
</div>


Vertical:

This is a bit tricky to achieve without flex layout. A table layout would not work here mainly because, the table-row would not keep a fixed height as required by your use-case. The height on a table-row or table-cell is only an indicative of the minimum height required. If the space is constrained, or the content exceeds the available space, then the cell or row will increase its height depending on the content.

As per the specs here: http://www.w3.org/TR/CSS21/tables.html#height-layout

The height of a 'table-row' element's box is calculated once the user agent has all the cells in the row available: it is the maximum of the row's computed 'height', the computed 'height' of each cell in the row, and the minimum height (MIN) required by the cells...

...the height of a cell box is the minimum height required by the content

This effect can be seen here: http://jsfiddle.net/abhitalks/6eropud3/

(Resize the window pane and you will see that the first row will increase in height as the content cannot be fit into the specified height, hence defeating the purpose)

Therefore, you can restrict the height indirectly either using inner markup like a div element, or let go of the table-layout and calculate the height for the flexible one. In your use-case, you prefer not to change the markup, hence I am not proposing an inner markup.

The best-bet here would be to use the time-tested model of plain block-level divs with the height of the flexible one to be calculated. As you have already discovered that it is not possible with CSS, you will need a small JavaScript snippet to do that for you.

A simple JavaScript snippet (no jQuery) which you could wrap in a window.load and drop into your project (and be done with) would look like this:

var flexv = document.querySelectorAll('div.flexv');
/* iterate the instances on your page */    
[].forEach.call(flexv, function(div) {
    var children = [].slice.call(div.children), // get all children
        flexChild = children.splice(-1, 1),     // get the last child
        usedHeight = 0, totalHeight = div.offsetHeight;

    children.forEach(function(elem) {
        usedHeight += elem.offsetHeight; // aggregate the height
    });
    /* assign the calculated height on the last child */
    flexChild[0].style.height = (totalHeight - usedHeight) + 'px';
});

The CSS snippet is more or less like the horizontal one, sans table layout, which also you could just drop into your project and just add the additional site-specific styling. Minimal markup required remains the same.

Demo Fiddle 2: http://jsfiddle.net/abhitalks/Ltcuxdwf/

Demo Snippet:

document.addEventListener("load", flexit);

function flexit(e) {
	var flexv = document.querySelectorAll('div.flexv');
	[].forEach.call(flexv, function(div) {
		var children = [].slice.call(div.children), 
			flexChild = children.splice(-1, 1), 
			usedHeight = 0, totalHeight = div.offsetHeight;
		children.forEach(function(elem) {
			usedHeight += elem.offsetHeight;
		});
		flexChild[0].style.height = (totalHeight - usedHeight) + 'px';
	});
}
div.flexv {
    display: inline-table; box-sizing: border-box; padding: 0; margin: 0; 
    overflow: hidden;
    /* Override your custom styling below */
    height: 320px; width: 20%; border: 1px solid black; font-size: 1em;
    margin: 8px;
}
div.flexv > div { 
    display: block; height: auto; box-sizing: border-box; 
    overflow: hidden;
    /* Override your custom styling below */
    background-color: lightgreen; border: 1px solid #ddd;
    padding: 5px 15px;
}
div.flexv > div:first-child {
    /* Override your custom styling below */
    min-height: 36px; height: 36px; max-height: 36px; 
    background-color: orange;
}
div.flexv > div:last-child {
    height: 100%;
    /* Override your custom styling below */
    background: skyblue;
}
<div class="flexv">
    <div>36px Fixed Height</div>
    <div>Variable Content Height</div>
    <div>Flexible Remaining Height</div>
</div>

<div class="flexv">
    <div>36px Fixed Height</div>
    <div><img src='//placehold.it/64x72/66c' /></div>
    <div>Flexible Remaining Height</div>
</div>

<div class="flexv">
    <div>36px Fixed Height</div>
    <div>Variable Text Height</div>
    <div>
        <img src='//placehold.it/72x48/66c' />
        <p>Variable Content Height</p>
    </div>
    <div>Flexible Remaining Height</div>
</div>

Note: As pointed out by @LGSon, the display: inline-table used for the demo does not play well with Firefox. This is only for a demo and should be replaced by either block or inline-block as per your use-case.