Does Class Order in HTML Affect CSS Priority?

Impact of Class Ordering on CSS Priority

While CSS selectors prioritize specificity based on element types and identifiers (#idname > .classname), the question arises whether the order of classes on a DOM element affects this priority.

Generally speaking, the ordering of HTML classes does not typically impact style precedence. For instance, the following HTML elements:

<div>
<p>Will have equivalent styling if the CSS rules are like:</p>
<pre class="brush:php;toolbar:false">.class1 { color: red; }
.class2 { color: blue; }

However, there are exceptions where HTML order can influence statement priority when using attribute selectors in CSS.

Attribute Selectors and Class Ordering

Attribute selectors target elements based on the presence or value of attributes, and the order of classes in HTML can affect how these selectors apply. For example:

Example 1 (Attribute Value Match):

[class="class1"] {
    color: red;
}

[class="class1 class2"] {
    background-color: yellow;
}

[class="class2 class1"] {
    border: 1px solid blue;
}

In this case, the order of classes in HTML matters when using the [class="value"] selector to match an exact attribute value. For instance:

<div>
<p>Will have a red font color because the [class="class1"] selector matches the attribute value, but the [class="class1 class2"] selector does not.</p>
<p>Similarly, for other attribute selectors like [class^="value"], [class$="value"], and [class~="value"], the order of classes in HTML can impact whether the selector applies and thus affects the applicable styles.</p>
<p><strong>Priority Clarification</strong></p>
<p>It's important to note that "priority" in this context refers to whether a CSS rule actually applies to an element, rather than assigning a higher priority to one rule over another. The order of classes can influence which attribute selectors match and, therefore, which rules apply to an element.</p>
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