HTML & CSS - - By Craig Buckler

How to Apply CSS3 Transforms to Background Images

CSS3 Transforms on Background Images

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Updated version of article published on September 27, 2012. Updates include latest data on current browser support, removing unnecessary vendor prefixes from code samples, and addition of live demo on CodePen.

Scaling, skewing and rotating any element is possible with the CSS3 transform property. It’s supported in all modern browsers without vendor prefixes. If you need to support Blackberry Browser and UC Browser for Android, you’ll need to use the -webkit- prefix, e.g.

#myelement {
  -webkit-transform: rotate(30deg);
  transform: rotate(30deg);
}

Great stuff. However, this rotates the whole element — its content, border and background image. What if you only want to rotate the background image? Or what if you want the background to remain fixed while the element is rotated?

Currently, there’s no W3C proposal for background-image transformations. It would be incredibly useful so I suspect one will appear eventually, but that doesn’t help developers who want to use similar effects today.

Fortunately, there is a solution. In essence, it’s a hack which applies the background image to a before or after pseudo element rather than the parent container. The pseudo element can then be transformed independently.

Transforming the Background Only

The container element can have any styles applied but it must be set to position: relative since our pseudo element will be positioned within it. You should also set overflow: hidden unless you’re happy for the background to spill out beyond the container.

#myelement {
  position: relative;
  overflow: hidden;
}

We can now create an absolutely-positioned pseudo element with a transformed background. The z-index is set to -1 to ensure it appears below the container’s content.

#myelement:before {
  content: "";
  position: absolute;
  width: 200%;
  height: 200%;
  top: -50%;
  left: -50%;
  z-index: -1;
  background: url(background.png) 0 0 repeat;
  -webkit-transform: rotate(30deg);
  transform: rotate(30deg);
}

Note you may need to adjust the pseudo element’s width, height and position. For example, if you’re using a repeated image, a rotated area must be larger than its container to fully cover the background:

CSS3 transformation on background

Fixing the Background on a Transformed Element

All transforms on the parent container are applied to pseudo elements. Therefore, we need to undo that transformation, e.g. if the container is rotated by 30 degrees, the background must be rotated -30 degrees to return to a fixed position:

#myelement {
  position: relative;
  overflow: hidden;
  -webkit-transform: rotate(30deg);
  transform: rotate(30deg);
}

#myelement:before {
  content: "";
  position: absolute;
  width: 200%;
  height: 200%;
  top: -50%;
  left: -50%;
  z-index: -1;
  background: url(background.png) 0 0 repeat;
  -webkit-transform: rotate(-30deg);
  transform: rotate(-30deg);
}

Again, you will need to adjust the size and position to ensure the background adequately covers the parent container.

Here are the relevant demos live on CodePen:

See the Pen CSS3 Transforms on Background Images by SitePoint (@SitePoint) on CodePen.

The effects work in all major browsers and in Edge and Internet Explorer back to version 9. IE8 will not show any transformations but the background still appears.

IE6 and 7 do not support pseudo elements so the background disappears. However, to support those ancient browsers, you could apply a background image to the container then set it to “none” using an advanced selector or conditional CSS.

CSS3 transforms lend themselves to tons of creative applications. Any particular one you’d like to share?

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