This is the third post in a series examining modern CSS solutions to problems I've been solving over the last 13+ years of being a frontend developer. Visit ModernCSS.dev to view the whole series and additional resources.
In the not to distant past when jQuery was King of the Mountain and CSS3 was still worth being designated as such, the most popular tool for responsive background images was the Backstretch jQuery plugin.
I used this plugin on ~30 sites prior to the following property becoming more supported (aka IE < 9 dropping in total market share):
background-size: cover;
According to caniuse.com, this property and value have been well supported for over 9 years! But websites that are intertwined with using Backstretch or another homegrown solution may not yet have updated.
The alternative method makes use of the standard img
tag, and uses the magic of:
object-fit: cover;
Let's look at how to use each solution, and learn when to select one over the other.
Using background-size: cover
A decade of my background was creating highly customized WordPress themes and plugins for enterprise websites. So using the example of templated cards, here's how you might set up using the background-size: cover
solution.
First, the HTML, where the image is inserted into the style
attribute as a background-image
. An aria-label
is encouraged to take the place of the alt
attribute that would normally be present on a regular img
tag.
<article class="card">
<div class="card__img" aria-label="Preview of Whizzbang Widget" style="background-image: url(https://placeimg.com/320/240/tech)"></div>
<div class="card__content">
<h3>Whizzbang Widget SuperDeluxe</h3>
<p>
Liquorice candy macaroon soufflé jelly cake. Candy canes ice cream
biscuit marzipan. Macaroon pie sesame snaps jelly-o.
</p>
<a href="#" class="button">Add to Cart</a>
</div>
</article>
The relevant corresponding CSS would be the following, where padding-bottom
is one weird trick that is used to set a 16:9 ratio on the div containing the image:
.card__img {
background-size: cover;
background-position: center;
// 16:9 ratio
padding-bottom: 62.5%;
}
Here's this solution altogether:
Using object-fit: cover
This solution is a newer player, and is not available to you if you need to support IE < Edge 16, according to caniuse data without a polyfill.
This style is placed directly on the img
tag, so we update our card HTML to the following, swapping the aria-label
to alt
:
<article class="card">
<img class="card__img" alt="Preview of Whizzbang Widget" src="https://placeimg.com/320/240/tech"/>
<div class="card__content">
<h3>Whizzbang Widget SuperDeluxe</h3>
<p>
Liquorice candy macaroon soufflé jelly cake. Candy canes ice cream
biscuit marzipan. Macaroon pie sesame snaps jelly-o.
</p>
<a href="#" class="button">Add to Cart</a>
</div>
</article>
Then our updated CSS swaps to using the height
property to constrain the image so that any size image conforms to the constrained ratio. If the inherent size of the image is greater than the constrained image size, the object-fit
property takes over and by default centers the image within the bounds created by the card container + the height
definition:
.card__img {
object-fit: cover;
height: 30vh;
}
And here's the result:
When to Use Each Solution
If you have to support older versions of IE, then without a polyfill you are limited to the background-size
solution (it pains me to say this in 2020, but this is a possibility particularly for enterprise and education industries).
Both solutions enable a full-width responsive image based on a width:height ratio you control.
Choose background-size
if:
- applying to a container expected to hold additional content, ex. a website header background
- to apply additional effect styles via pseudo elements which are not available to the
img
element - to more gracefully apply a uniform size of image
- the image is purely decorative and the inherent
img
semantics are not needed
Choose object-fit
if:
- using a standard
img
is best for your context in order to maintain all semantics provided by an image
Top comments (1)
Hi Stephanie, thanks for your inspiring serie of html/css. I noticed that the outcome of those two full-width responsive images methods is quite different. It is already to see in your pens, but I made an example in which you can see the difference better: jaswa.nl/docs/aaa/objectfit-vs-bg....
Cheers from Amsterdam, Jaap Swart