How Can I Apply Opacity to a CSS Color Variable While Preserving Background Images?

How to Apply Opacity to a CSS Color Variable

The Challenge:

When designing an app with CSS variables, you may encounter the need to apply opacity to a defined color variable. However, standard CSS opacity doesn't suffice as you want to preserve the background image.

The Solution: RGBA Manipulation

CSS custom properties allow for a unique solution. By converting the hex color value into an RGB triplet using commas, you can store it as a custom property. Using the var() function, you can substitute this value into an rgba() function, specifying the desired alpha value.

For instance, given a color variable:

:root {
  --color: #f0f0f0;
}

You can apply 80% opacity to it with:

#element {
  background-color: rgba(var(--color), 0.8);
}

This results in:

<p></p>

where the background color of the element has 80% opacity while maintaining the background image.

Implementation Note:

This method is supported by all major browsers. However, it's worth noting that it converts the hex value to decimal RGB, which may affect the accuracy of the color representation in some situations.

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