How deep can nesting go within a CSS rule?

When working with stylesheets, the majority of CSS rules follow a structured format:

selector {
    property_1 : value_1;
    .
    .
    .
    property_n : value_n;
}

Each selector typically has only one {} block attached to it (without any sub {} blocks inside), which we can refer to as degree of nesting = 1.

However, when it comes to at-rules, we encounter more complex structures like this:

@media screen and (min-width:1000px) {

    body {
        font-size: 20px;  
    }

}

In such cases, there is a nested CSS block within the @media rule, increasing the degree of nesting to 2.

The highest level of nesting I have seen is with a nesting degree of 3, demonstrated here:

@media screen and (min-width:1000px) {
    
    @keyframes myidentifier {

        0%   { top: 0; left: 0; }
        100% { top: 100px; left: 100%; }

    }

}

It raises the question: Can CSS blocks be nested even deeper than this example?

Answer №1

You have the flexibility to nest Conditional CSS Rules as deeply as you wish:

@media print {
  @media (max-width: 12cm) {
    /* ... */
  }
}

Answer №2

Building on Jeff's response:

In traditional CSS, style rules (previously known as rulesets) - which consist of selectors and property-value declarations - cannot be nested. There is a proposed specification called css-nesting that aims to introduce this feature from popular stylesheet preprocessors to standard CSS, but it has not been finalized yet.

Conditional at-rules like @media and @supports can be nested within one another without limitation. It is even possible to nest one inside the other. Previously, in CSS2.1, nesting @media at-rules was not allowed, but this restriction has been lifted in css-conditional-3, with a section detailing how conditional rules can be nested.

However, this nesting capability does not extend to all at-rules with blocks. For instance, @keyframes at-rules are not conditional rules; they can be nested within @media or @supports rules to any depth, but cannot contain conditional rules or other @keyframes rules. They are only permitted to contain keyframe blocks, such as the 0% and 100% blocks in your example.

As new modules are introduced into CSS, new at-rules may come with their own defined nesting restrictions outlined in their respective specifications. Nevertheless, anything specified in css-conditional-3 can be nested freely and interchangeably to any level of depth.

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