CSS Background shorthand coming to mobile WebKit browsers

Earlier this year, WebKit updated the behavior of the CSS background shorthand property. With this change, the background shorthand property will reset the background-size to its default value of auto auto if it’s not set in the shorthand declaration. This change brings Chrome and other WebKit browsers in compliance with the specification and matches the behavior of Firefox, Opera and Internet Explorer.

With Chrome for Android moving forward to current revisions on WebKit, this change is now rolling out in Android. Because this was a fix to webkit, sites that tested in multiple browsers are likely not affected.

Old way of doing things

// background-size is reset to auto auto by the background shorthand
.foo {
    background-size: 50px 40px;
    background: url(foo.png) no-repeat;

The background shorthand property does not contain any size property and will therefore reset the background-size to its default value of auto auto.

Correct way to specifying image size

// background-size is specified after background
.fooA {
    background: url(foo.png) no-repeat;
    background-size: 50px 40px;

// background-size is specified inline after position
.fooB {
    background: url(foo.png) 0% / 50px 40px no-repeat;

In fooB, specifying a background-size in the background shorthand requires the position (0%) be specified first, followed by a forward slash then the background-size (50px 40px).

Fixes for existing code

There are several options that will provide an easy fix for this:

  • Use background-image instead of the background shorthand property.
  • Set the background-size last, with a higher specificity than any other CSS rules that set background on that element, and don’t forget to check and :hover rules.
  • Apply the !important property to background-size.
  • Move the sizing information to the background shorthand property.

Bonus: background image offsets

In addition to this change, there’s now greater flexibility in positioning the image within the background. In the past, you could only specify the image position relative from the top left corner, now you can specify an offset from the edges of the container. For example setting background-position: right 5px bottom 5px; the image will be positioned 5px from the right edge and 5px from the bottom. Check out this sample on JSBin