Did you know that CSS Custom Properties can handle images too?

So you might be aware of CSS Custom Properties that let you set a variable, such as a theme color, and then apply it to multiple classes like this:

:root {
  --theme: #777;
}

.alert {
  background: var(—-theme);
}

.button {
  background: var(—-theme);
}

Well, I had seen this pattern so often that I thought Custom Properties could only be used for color values like rgba or hex – although that’s certainly not the case! After a little bit of experimentation and sleuthing around, I realized that it’s possible to use Custom Properties to set image paths, too.

Here’s an example of that in action:

:root {
  --errorIcon: url(error.svg)
}

.alert {
  background-image: var(--errorIcon);
}

.form-error {
  background-image: var(--errorIcon);
}

Kinda neat, huh? I think this could be used to make an icon system where you could define a whole list of images in the :root and call it whenever you needed to. Or you could make it easier to theme certain classes based on their state or perhaps in a media query, as well. Remember, too, that custom properties can be overridden within an element:

:root {
  --alertIcon: url(alert-icon.svg)
}

.alert {
  background-image: var(--alertIcon);
}

.form-error {
  --alertIcon: url(alert-icon-error.svg)
  background-image: var(--alertIcon);
}

And, considering that custom properties are selectable in JavaScript, think about the possibilities of swapping out images as well. I reckon this might useful to know!

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