width

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Sara Cope on (Updated on )

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The width property in CSS specifies the width of the element’s content area. This “content” area is the portion inside the padding, border, and margin of an element (the box model).

.wrap { 
  width: 80%;
}

In the example above, elements that have a class name of .wrap will be 80% as wide as their parent element. The accepted values are any of the length values, in addition to some keywords we’ll cover later.

Width can be overridden by the closely correleated properties min-width and max-width.

.wrapper-1 {
  width: 100%;
  max-width: 320px; /* Will be AT MOST 320px wide */
}

.wrapper-2 {
  width: 100%;
  min-width: 20em; /* Will be AT LEAST 20em wide */
}

Digging deeper

When using percentage (%) for width, authors must be aware that the percentage is based on the element’s parent, or in other words, the width of the containing block. If your parent is set at 480px – as demonstrated by our demo – then the percentage is based on that value. So in our case 50% of 480px leaves us with 240px as a computed pixel value.

Note that width applies to all elements except non-replaced or inline elements, table rows and row groups (i.e. thead, tfoot and tbody). There seems to be a slight mismatch as far as how HTML defines non-replaced elements and how CSS defines it, but we’re referring to it the way CSS does: elements whose content is not defined by the tag itself, such as an <img> with the src attribute.

For absolutely positioned elements whose containing block is based on a block container element, the percentage is calculated with respect to the width of the padding box of that element.

Keyword values

With some special keyword values, it is possible to define width (and/or height) according to the content of the element.

min-content

The min-content value is the smallest measure that would fit around its content if all soft wrap opportunities within the box were taken.

The best example for this kind of value is a properly written figure element:

What a lovely kitten we got there in this image which is encapsulated in a figure element. How dear, look how long this caption is!

Once we have applied some basic styles to this markup, we get:

If we wanted that figure element to essentially be the size of that image, so the text wraps at the edges of the image. We could float it left or right, because float will exhibit that same kind of shrink-to-fit behavior, but what if we wanted to center it? min-content allows us to center it:

Because we’ve assigned min-content to the figure element, it takes the minimum width it can have when taking all soft wrap opportunities (like spaces between words) so that the content still fits in the box.

max-content

The max-content property refers to the narrowest measure a box could take while fitting around its content – if no soft wrap opportunities within the element were taken.

Check out what happens if we apply this to our simple kitten/figure demo:

Because the caption is very longer than the image is wide (it doesn’t take any soft wrap opportunity, like the spaces between words), it means it has to display the caption on a single line, thus the figure is as wide as that line.

fill-available

???. One of life’s great mysteries.

fit-content

The fit-content value is roughly equivalent to margin-left: auto and margin-right: auto in behaviour, except it works for unknown widths.

For instance, let’s say we need to center an inline navigation across the page. Your best bet would be to apply text-align: center to the ul, and display: inline-block to the li. This would give you something like this:

However, the blue background (from the ul element) spreads across the entire document because the ul is a block-level element, which means its width is restricted only by its containing element. What if we want to have the blue background collapsing around the list items? fit-content to the rescue!

With fit-content and margin: 1em auto, this works like a charm and only the navigation has a colored background, not the whole document width.

If you’re into this sort of thing, you’ll be happy to know the formula to define the size of a fit-content length is:

fit-content = min(max-content, max(min-content, fill-available))

This is a pretty unused value, so if you come up with a great use-case, let us know!

Browser support

IEEdgeFirefoxChromeSafariOpera
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Android ChromeAndroid FirefoxAndroid BrowseriOS SafariOpera Mobile
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Source: caniuse

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