How Can I Dynamically Assign Units to CSS Variables?

Dynamic Unit Assignment to CSS Variables

In CSS, the ability to utilize variables offers significant flexibility and maintainability. However, assigning unitless values to variables can present challenges when using them for different purposes. This article addresses the issue of setting a CSS variable with a numeric value and subsequently assigning units dynamically based on usage.

Consider the following example:

--mywidth: 10;

div {
  width: var(--mywidth) + %;  // should be => width: 10%
}

The goal is to use the --mywidth variable as a percentage for certain CSS properties and as a number for others, such as calc() operations.

The solution lies in leveraging the power of calc(). By performing a simple multiplication between the variable and the desired unit, you can dynamically assign units as needed.

div {
  width: calc(var(--mywidth) * 1%);
}

This approach ensures that the variable retains its numerical value while allowing you to specify units based on the specific property you are using.

For instance, consider the following example:

:root {
  --a: 50;
}

.box {
  width: calc(var(--a) * 1%);  // 50%
  border: calc(var(--a) * 0.5px) solid red;  // 25px
  background: linear-gradient(calc(var(--a) * 0.8deg), blue 50%, green 0);  // 40deg gradient
  padding: 20px;  // 20px
  box-sizing: border-box;
}

In this example, the --a variable is used throughout the .box class, with units dynamically assigned using calc().

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