rhombidodecahedron rhombidodecahedron - 11 months ago 91
CSS Question

HTML background image offset by x pixels from the center

I'd like to put an image as the background of a webpage but have it offset by some number of pixels with respect to the center.

How can I do this?

I want:

background-image: url("bg.png");
background-position: 25% center;
background-attachment: fixed;
background-repeat: no-repeat;

but instead of 25%, I want something along the lines of "center - 50px". Is there any solution to this?

Answer Source

I believe I have a solution that achieves what you're wanting:

A background image (specifically a page background) offset by a number of pixels with respect to the center.

This works using only HTML & CSS - no javascript.


#background-container {
    width: 100%;
    left: -100px; /* this must be TWICE the required offset distance*/
    padding-right: 100px; /* must be the same amount as above */

    background-image: url("background-image.png");
    background-position: center;
    background-repeat: no-repeat;

What this does is moves the the entire container horizontally by the amount specified (in this case to the left 100px). Because the background image is centered relative to the container it moves to the left with the container.

The padding fixes the 100px of blank space that would appear to the right of the container as a result of the move. Background images show through padding). Because browsers use the border-box value instead of the default content-box value to calculate background sizing and positioning, the background image is effectively moved back to the right 50px - half the distance of the padding. (Thanks to ErikE for clarification).

So your offset/padding must be twice the required offset distance.

I have prepared a sample page for you here: http://www.indieweb.co.nz/testing/background-offset-center.html

Have a play with resizing the window. You will see that the purple and blue background image (laid over a deeper background image marking the center of the page) remains exactly 50px (half the offset/padding distance) to the left of the page center.

UPDATE This can now be easily achieved using background-position and calc as a CSS unit. Don't use this method if you require support for legacy versions of IE.

The following CSS will achieve the same outcome as the previous CSS block:

#background-container {
    width: 100%;

    background-image: url("background-image.png");
    background-position: calc(50% - 50px) 50%;
    background-repeat: no-repeat;