Don't Fight the Cascade, Control It!

Master the CSS cascade: Say goodbye to chaos and embrace control! This article will explore how to use new CSS features to control cascades to write more concise and efficient CSS code. In the past, styles from different sources often made cascades difficult to manage and eventually produced redundant code. Even with methods like ITCSS and BEM, we still face challenges posed by cascades, such as the need to precisely control the position of the @import statement or have to resort to !important . Fortunately, some new tools have come out, allowing us to effectively control the cascade.

Drive :where pseudo selector

:where pseudo-selectror allows us to remove the particularity of the selector so that it is only higher than the user agent default style, regardless of the CSS loading order. This means that the selector's particularity is actually zero, which is very useful for general-purpose components.

For example, use :where to define a common table style:

 :where(table) {
  background-color: tan;
}

Even if other table styles were defined before this:

 table {
  background-color: hotpink;
}

:where(table) {
  background-color: tan;
}

The table background color is still tan because :where eliminates the particularity of the selector. This makes :where perfect for CSS reset.

:where 's brother selector :is has the opposite effect:

The particularity of the :is() pseudo-class is determined by the particularity of its most special parameters. Therefore, selectors written with :is() do not necessarily have the same speciality as equivalent selectors written without :is() . ——Selector Level 4 Specification

Continue with the previous example:

 :is(table) {
  --tbl-bgc: orange;
}
table {
  --tbl-bgc: tan;
}
:where(table) {
  --tbl-bgc: hotpink;
  background-color: var(--tbl-bgc);
}

The background color of the table will be tan because :is has the same particularity as table , and table is located behind it. But if we change it to:

 :is(table, .c-tbl) {
  --tbl-bgc: orange;
}

The background color will be orange because :is has the same weight as its most special selector.c .c-tbl .

Example: Configurable table components

Let's build a table component with the following HTML:

Next, we wrap .c-tbl in :where selector and add the rounded corners:

 :where(.c-tbl) {
  border-collapse: separate;
  border-spacing: 0;
  table-layout: auto;
  width: 99.9%;
}

Table cells use different styles:

 :where(.c-tbl thead th) {
  /* ... */
}
:where(.c-tbl tbody td) {
  /* ... */
}

Due to rounded corners and border-collapse: separate , we need to add extra styles:

 :where(.c-tbl tr td:first-of-type) {
  /* ... */
}
/* ... */

Now we can create variations of the table component by injecting other styles before or after the general style (benefits from :where 's speciality elimination):

 .c-tbl--purple th {
  background-color: hsl(330, 50%, 40%)
}
/* ... */

CSS custom properties

We will use data-component property to define the component:

Generic styles will be applied to all component instances, and styles for specific component instances will be included in the general class, and custom properties of the common component are used.

 :where([data-component="table"]) {
  /* ... */
}
.c-tbl--purple {
  /* ... */
}

In a common component, each CSS property points to a custom property. Attributes that need to act on child elements (such as border-color ) are specified at the root of the general component:

 :where([data-component="table"]) {
  --tbl-hue: 200;
  /* ... */
}
:where([data-component="table"] td) {
  border-color: var(--tbl-bdc);
}

Other properties can be set static values ​​or configured using custom properties. If using custom properties, remember to define a default value for use when variant classes are missing.

 :where([data-component="table"]) {
  background-color: var(--tbl-bgc, transparent);
  /* ... */
}

We can use custom properties to control column alignment and width:

 :where([data-component="table"] tr > *:nth-of-type(1)) {
  text-align: var(--ca1, initial);
  /* ... */
}

Now, let's create a specific component style, using the regular class .c-tbl :

 .c-tbl {
  --tbl-hue: 330;
}

We just need to update the properties without writing a brand new CSS! Change a property to update the color of the table.

We can write more complex styles, such as zebra stripes:

 .c-tbl tr:nth-child(even) td {
  --tbl-td-bgc: hsl(var(--tbl-hue), var(--tbl-sat), 95%);
}

Add parameters using another data-attribute

We can add another data-param property to add more parameters:

Then, in CSS we can use the property selector to match the entire word in the parameter list. For example, a zebra stripe row:

 [data-component="table"][data-param~="zebrarow"] tr:nth-child(even) td {
  --tbl-td-bgc: var(--tbl-zebra-bgc);
}

Or zebra stripes column:

 [data-component="table"][data-param~="zebracol"] td:nth-of-type(odd) {
  --tbl-td-bgc: var(--tbl-zebra-bgc);
}

Cascade layer

The last tool to control cascade is the "cascade layer". Currently, it is an experimental feature that can be accessed in Safari or Chrome to enable the #enable-cascade-layers flag.

The cascade layer allows us to inject style sheets in a specific order. A simplified structure is as follows:

 @layer generic, components;

This determines the order of the layers. First there is a general style, then component-specific style.

Even if the component style is written before the general style, the component style layer still takes precedence:

 @layer components {
  body {
    background-color: lightseagreen;
  }
}

@layer generic { 
  body {
    background-color: tomato;
  }
}

Summarize

:where and :is pseudo-selecters allow us to control specificity; CSS custom attributes allow us to override styles without writing new classes; data-attribute allow us to increase flexibility; cascades allow us to specify the loading order of styles. CSS cascade is no longer an enemy, but a tool we can control.

Image from Stephen Leonardi on Unsplash

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