Atlas Atomics

Welcome to Atomics ⚛! These are small, single purpose, CSS classes that can be used to compose great things. Visit this article for a longer definition of Atomic CSS here.

Categories of classes

Most of our classes fall into one of several categories. Those that affect ...

  • display (ex. .display-inline-flex)
  • spacing (ex. .margin-inline-lg);
  • color (ex. .color-primary)
  • typography (ex. .font-size-md);
  • flex properties (ex. .justify-content-center)
  • and more ...

Naming patterns

All of our atomic classes try to follow the same pattern.

// or

CSS Property Values

The first part of nearly every Atomic class represent the css property that it will modify. For example, display in the class .display-flex matches the property value from the corresponding css rule display: flex;. We hope this will provide a clear and easily intuited pattern for our Atomics and encourage everyone to learn the fundamentals of CSS.


While CSS properties are straightfoward (they just match the CSS), the value property is not always as easy to guess. We have a few rules that help us figure out how to write values in class names.

  1. When the CSS value is a string (such as flex-end in justify-content: flex-end, or grid in display: grid;) then we just use that string directly (meaning these classes become .justify-content-flex-end and .display-grid).
  2. In some cases, such as themed colors values, values are associated concepts.
    • Such as primary in the class .color-primary. (The primary is blue on light theme and yellow on high contrast theme.)
    • Such as semibold in the class font-weight-semibold.
  3. When a value refers to a pixel value is involved we will just write out the number.
    • Some width based classes use this approach. width-100 means width: 100px.
  4. When a em/rem value is involved, that value is typically represented as an at-least-two-letter-t-shirt size.
    • Spacing and non-heading typography values follow this convention, as in xs, sm, md, lg, xl, xxl in margin-top-xl, and font-size-md.
    • Within a set of values that require units such as the one above, 0 is represented by the string none.
  5. Within a series of values that are all unitless numbers, those numbers are used directly, as in flex-grow: 1; being represented by flex-grow-1.
  6. When a shorthand property's value is multi-part, we choose a reasonable default and omit the value completely.
    • In the case border: 1px solid $border the class becomes simply .border.
    • In this case further modification would still be available.

Screen sizes

Screen sizes are represented by one of the following strings:

  • tablet, representing screens tablet and larger.
  • desktop, representing screen desktop width and larger.
  • widescreen, representing very wide screens to infinity.

Use a mobile first approach when using Atomics, including the universally applicable class (i.e. the one that does not have a screensize at the end), and when necessary overwrite its values on larger screens.