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Recreating `border-image` with `background-image` for the curious

jsnkuhn
・1 min read

Since border-image was first introduced around 2010 to this day I've received one consistent comment from my fellow developers any time I use it:

Why not just use background-image instead?

So here it is folks! Here's the default border-image code versus what you'd have to do in background-image to get the same result. This is why I don't do that!

border: solid 27px;
border-image: url('border.png') 27; 
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Equivalent background image code:

/* don't do this */
background: 
  url('top-left-corner.png') 0 0 / 20px 20px no-repeat, 
  url('top-right-corner.png') 100% 0 / 20px 20px no-repeat,
  url('bottom-left-corner.png') 0 100% / 20px 20px no-repeat,
  url('bottom-right-corner.png') 100% 100% / 20px 20px no-repeat,
  url('left-border.png') 0 20px / 20px calc(100% - 40px) no-repeat,
  url('right-border.png') 100% 20px / 20px calc(100% - 40px) no-repeat,
  url('top-border.png') 20px 0 / calc(100% - 40px) 20px no-repeat,
  url('bottom-border.png') 20px 100% / calc(100% - 40px) 20px no-repeat;
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Discussion (6)

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abhinav1217 profile image
Abhinav Kulshreshtha

I don't any benefit of doing this? If you could provide a codepen or before-after screenshot of final output, maybe it could provide some context on why would someone choose to make 8 network calls for something which ideally shouldn't even need it.

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jsnkuhn profile image
jsnkuhn Author

Codepen is now included.

To be fair if the border-image-source begin used is symmetrical you might only need 3 network requests (one for left/right border, one for top/bottom border and one for the corners)... Or with an SVG fragment identifiers could be used on 1 single image. But yes it's still likely much more work then just using border-image proper.

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afif profile image
Temani Afif

why doing this? I wouldn't call this an equivalent because all depend on the the image you will be using

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jsnkuhn profile image
jsnkuhn Author

The point is to show the absurdity of people's constant reaction to use of border-image with "why not just use background"

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afif profile image
Temani Afif

there is no absurdity. Each method has its use cases and you are not demonstrating anything by using a generic code. Better give a real example with a real image if you want to highlight a fact or to compare between both method.

Both code provided aren't equivalent at all.

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jsnkuhn profile image
jsnkuhn Author

Post updated with Codepen example to show the equivalence and an extra explanation to hopefully clear up some confusion.