@layer

The @layer CSS at-rule declares a cascade layer. Rules within a cascade layer cascade together, giving more control over the cascade to web developers.

@layer utilities {
  /* creates a named layer called utilities. */
}

The @layer at-rule is used to create a cascade layer in one of three ways. The first is as in the example above, creating a block at-rule with the CSS rules for that layer inside.

@layer utilities {
  .padding-sm {
    padding: .5rem;
  }

  .padding-lg {
    padding: .8rem;
  }
}

A cascade layer can be created with @import, in this case the rules would be in the imported stylesheet:

@import 'utilities.css' layer(utilities);

You can also create a named cascade layer without assigning any styles. This can be a single name:

@layer utilities;

Or, multiple layers can be defined at once. For example:

@layer theme, layout, utilities;

This is useful because the initial order in which layers are declared indicates which layer has precedence. As with declarations, the last layer to be listed will win if declarations are found in multiple layers. Therefore, with the preceding example, if a competing rule was found in theme and utilities the one in utilities would win and be applied.

The rule in utilities would be applied even if it has lower specificity than the rule in theme. This is because once layer order has been established, specificity and order of appearance are ignored. This enables the creation of simpler CSS selectors, as you do not have to ensure that a selector will have high enough specificity to override competing rules, all you need to ensure is that it appears in a later layer.

Any styles not in a layer are gathered together and placed into an anonymous layer that comes after all the declared layers. This means that any styles declared outside of a layer will override styles declared in a layer.

Layers may be nested. For example:

@layer framework {
  @layer layout {

  }
}

To append rules to the layout layer inside framework join the two names with a ..

@layer framework.layout {
  p {
    margin-block: 1rem;
  }
}

If a layer is created with no name, for example:

@layer {
  p {
    margin-block: 1rem;
  }
}

Then an anonymous, unnamed, layer is created. This functions in the same way as named layers, however rules cannot be assigned to it later.

@layer [ <layer-name># | <layer-name>?  {
  <stylesheet>
} ]

In the following example, two CSS rules are created. One for the <p> element outside of any layer and one inside a layer named type for .box p.

Without layers, the selector .box p would have the highest specificity and therefore the text Hello, world! will display in green. As the type layer comes before the anonymous layer created to hold non-layer content, the text will be purple.

Also notice order. Even though we declare the non-layered style first, it's still applied after the layer styles.

HTML

<div class="box">
  <p>Hello, world!</p>
</div>

CSS

p {
  color: rebeccapurple;
}

@layer type {
  .box p {
    font-weight: bold;
    font-size: 1.3em;
    color: green;
  }
}

Result

In the following example, two layers are created with no rules applied, then CSS rules are applied to the two layers. The base layer defines a color, border, font-size, and padding. The special layer defines a different color. As special comes last when the layers were defined, the color it provides is used and the text is displayed using rebeccapurple. All of the other rules from base still apply.

HTML

<div class="item">I am displayed in <code>color: rebeccapurple</code>
because the <code>special</code> layer comes after the <code>base</code> layer.
My green border, font-size, and padding come from the <code>base</code> layer.</div>

CSS

@layer base, special;

@layer special {
  .item {
    color: rebeccapurple;
  }
}

@layer base {
  .item {
    color: green;
    border: 5px solid green;
    font-size: 1.3em;
    padding: .5em;
  }
}

Result

• The Future of CSS: Cascade Layers