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The following web format is provided when compiling design tokens to CSS using web-css. It utilizes CSS variables for reusability. If you need to support legacy browsers, we suggest the css-vars-ponyfill library.

File structure#

During compilation, an index.css file will be created based on the design system YAML configuration file. Additional themes/<name>.css files will be created for each theme configured in the YAML file.

This would look something like the following:

├── themes/
│ ├── day.css
│ └── night.css
├── index.css


As mentioned above, a design system and multiple theme files are created. The design system file defines primitive variables, while each theme file defines color and palette variables, both of which rely on CSS variables.

The compiled design system file uses :root and looks something like the following:

:root {
--border-sm-radius: 0.11rem; /* 1.50px */
--border-sm-width: 0rem; /* 0px */
--border-df-radius: 0.21rem; /* 3px */
--border-df-width: 0.07rem; /* 1px */
--border-lg-radius: 0.32rem; /* 4.50px */
--border-lg-width: 0.14rem; /* 2px */
--breakpoint-xs-query: 'screen and (min-width: 45.71em)';
--breakpoint-xs-query-size: 640;
--breakpoint-xs-root-line-height: 1.33;
--breakpoint-xs-root-text-size: 14.94px;
--breakpoint-sm-query: 'screen and (min-width: 68.57em)';
--breakpoint-sm-query-size: 960;
--breakpoint-sm-root-line-height: 1.42;
--breakpoint-sm-root-text-size: 15.94px;
--breakpoint-md-query: 'screen and (min-width: 91.43em)';
--breakpoint-md-query-size: 1280;
--breakpoint-md-root-line-height: 1.52;
--breakpoint-md-root-text-size: 17.01px;
--breakpoint-lg-query: 'screen and (min-width: 114.29em)';
--breakpoint-lg-query-size: 1600;
--breakpoint-lg-root-line-height: 1.62;
--breakpoint-lg-root-text-size: 18.15px;
--breakpoint-xl-query: 'screen and (min-width: 137.14em)';
--breakpoint-xl-query-size: 1920;
--breakpoint-xl-root-line-height: 1.73;
--breakpoint-xl-root-text-size: 19.36px;
--depth-content: 100;
--depth-navigation: 1000;
--depth-sheet: 1100;
--depth-overlay: 1200;
--depth-modal: 1300;
--depth-toast: 1400;
--depth-dialog: 1500;
--depth-menu: 1600;
--depth-tooltip: 1700;
--heading-l1-letter-spacing: 0.25px;
--heading-l1-line-height: 1.5;
--heading-l1-size: 1.14rem; /* 16px */
--heading-l2-letter-spacing: 0.33px;
--heading-l2-line-height: 1.69;
--heading-l2-size: 1.43rem; /* 20px */
--heading-l3-letter-spacing: 0.44px;
--heading-l3-line-height: 1.9;
--heading-l3-size: 1.79rem; /* 25px */
--heading-l4-letter-spacing: 0.59px;
--heading-l4-line-height: 2.14;
--heading-l4-size: 2.23rem; /* 31.25px */
--heading-l5-letter-spacing: 0.79px;
--heading-l5-line-height: 2.4;
--heading-l5-size: 2.79rem; /* 39px */
--heading-l6-letter-spacing: 1.05px;
--heading-l6-line-height: 2.7;
--heading-l6-size: 3.49rem; /* 48.80px */
--shadow-xs-x: 0rem; /* 0px */
--shadow-xs-y: 0.14rem; /* 2px */
--shadow-xs-blur: 0.14rem; /* 2px */
--shadow-xs-spread: 0rem; /* 0px */
--shadow-sm-x: 0rem; /* 0px */
--shadow-sm-y: 0.23rem; /* 3.24px */
--shadow-sm-blur: 0.27rem; /* 3.75px */
--shadow-sm-spread: 0rem; /* 0px */
--shadow-md-x: 0rem; /* 0px */
--shadow-md-y: 0.37rem; /* 5.24px */
--shadow-md-blur: 0.39rem; /* 5.50px */
--shadow-md-spread: 0rem; /* 0px */
--shadow-lg-x: 0rem; /* 0px */
--shadow-lg-y: 0.61rem; /* 8.47px */
--shadow-lg-blur: 0.52rem; /* 7.25px */
--shadow-lg-spread: 0rem; /* 0px */
--shadow-xl-x: 0rem; /* 0px */
--shadow-xl-y: 0.98rem; /* 13.71px */
--shadow-xl-blur: 0.64rem; /* 9px */
--shadow-xl-spread: 0rem; /* 0px */
--spacing-xs: 0.31rem; /* 4.38px */
--spacing-sm: 0.63rem; /* 8.75px */
--spacing-df: 1.25rem; /* 17.50px */
--spacing-lg: 2.5rem; /* 35px */
--spacing-xl: 3.75rem; /* 52.50px */
--spacing-unit: 17.5;
--text-sm-line-height: 1.25;
--text-sm-size: 0.89rem; /* 12.45px */
--text-df-line-height: 1.25;
--text-df-size: 1rem; /* 14px */
--text-lg-line-height: 1.25;
--text-lg-size: 1.13rem; /* 15.75px */
--typography-font-heading: 'Roboto';
--typography-font-monospace: '"Lucida Console", Monaco, monospace';
--typography-font-text: 'Roboto';
--typography-font-system: 'system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol"';
--typography-root-line-height: 1.25;
--typography-root-text-size: 14px;

While the compiled theme files look loosely like the below (removed some repetition for brevity). Do note that theme variables are scoped within a class name, not :root, and as such, cannot be polyfilled.

.theme-day {
--palette-brand-color-00: #eceff1;
--palette-brand-color-10: #cfd8dc;
--palette-brand-color-20: #b0bec5;
--palette-brand-color-30: #90a4ae;
--palette-brand-color-40: #78909c;
--palette-brand-color-50: #607d8b;
--palette-brand-color-60: #546e7a;
--palette-brand-color-70: #455a64;
--palette-brand-color-80: #37474f;
--palette-brand-color-90: #263238;
--palette-brand-bg-base: #78909c;
--palette-brand-bg-focused: #607d8b;
--palette-brand-bg-hovered: #546e7a;
--palette-brand-bg-selected: #607d8b;
--palette-brand-bg-disabled: #90a4ae;
--palette-brand-fg-base: #546e7a;
--palette-brand-fg-focused: #455a64;
--palette-brand-fg-hovered: #37474f;
--palette-brand-fg-selected: #455a64;
--palette-brand-fg-disabled: #607d8b;
--palette-brand-text: #37474f;


To activate a design system and theme, link the CSS file within your document to make the CSS variables available.

<link href="styles/<target>/index.css" rel="stylesheet" />
<link href="styles/<target>/themes/day.css" rel="stylesheet" />

With this pattern, only 1 design system may be active at a time, as they all rely on :root. However, multiple themes can be active at a time, as they are scoped by class name. To apply a theme to the entire document, add the class name to <body />, while nested themes can be applied to any child element.

<body class="theme-day" />
<div class="theme-night" />

If using a bundler like Webpack or Parcel, import the CSS file within the root entry point, or as early as possible.

import './styles/<target>/index.css';
import './styles/<target>/themes/day.css';


Since the CSS format is built around variables, we can utilize the var() function for reusability. Simply reference the variables listed above like so:

.button {
display: inline-block;
text-align: center;
font-size: var(--text-df-size);
line-height: var(--text-df-line-height);
padding: var(--spacing-sm) var(--spacing-df);
color: var(--palette-brand-fg-base);
background-color: var(--palette-brand-bg-base);
.button:hover {
color: var(--palette-brand-fg-hovered);
background-color: var(--palette-brand-bg-hovered);

And apply the classes to HTML as normal.

<button type="button" class="button">Continue</button>