CSS Variables

Using token-aware CSS variables in Fidely UI

Overview

CSS variables have become the defacto way to create shared values on the web. It's very useful to avoid prop interpolations, classname regeneration, and reduce runtime evaluation of token values.

Examples

Basic

Use the css prop to create css variables

<Box css={{ '--font-size': '18px' }}>
  <h3 style={{ fontSize: 'calc(var(--font-size) * 2)' }}>Hello</h3>
  <p style={{ fontSize: 'var(--font-size)' }}>Hello</p>
</Box>

Access tokens

Use the full token path to access tokens

<Box css={{ '--color': 'colors.red.9' }}>
  <p style={{ color: 'var(--color)' }}>Hello World</p>
</Box>

Here's an example of how to access size tokens

<Box css={{ '--size': 'sizes.12' }}>
  <p style={{ width: 'var(--size)', height: 'var(--size)' }}>Hello World</p>
</Box>

Responsive Styles

Use the responsive syntax to make css variables responsive

<Box css={{ '--font-size': { base: '16px', lg: '24px' } }}>
  <h3 style={{ fontSize: 'calc(var(--font-size) * 2)' }}>Hello</h3>
  <p style={{ fontSize: 'var(--font-size)' }}>Hello</p>
</Box>

Color Opacity Modifier

When accessing color tokens, you can use the opacity modifier to access the color with an opacity. The requirement is to use the syntax.

<Box css={{ '--color': '{colors.red.10/80}' }}>
  <p style={{ color: 'var(--color)' }}>Hello</p>
</Box>

Virtual Color

Variables can point to a virtual color via the colors.colorPalette.* value. This is useful for creating theme components.

<Box colorPalette="purple" css={{ '--color': 'colors.colorPalette.8' }}>
  <p style={{ color: 'var(--color)' }}>Hello</p>
</Box>