Error with mandatory attribute found in W3C CSS Validator

When using the W3C CSS 3 Validator, I encountered this error:

The :required pseudo-element or pseudo-class is unknown

The required attribute is used in HTML5 for input elements. Despite working in IE10, Google Chrome, and Firefox, my CSS still triggers this issue.

Here's a snippet of my CSS code:

#reserved input:required {background:#eaeae6;}
#reserved select:required {background:#eaeae6;}

As for my HTML code:

<section id="reserved">
    <select id="hab" name="hab" title="Study or Apartment" required>
    <input type="text" id="name" name="name" maxlength="50" style="width: 200px;" title="Name and Surname" required/>
</section>

Why isn't W3C acknowledging the required attribute as a standard?

csshtmlvalidation

Answer №1

The CSS3 specification features the Selectors Level 3 API, which does not include the Selectors Level 4 selector.

Introduced in Selectors Level 4, the :required selector is supported by browsers but is not included in the CSS3 specification. As a result, it will cause validation errors in a CSS3 validator.

Answer №2

Appreciate your input, solitaryday.

I decided to update my CSS by creating a new class instead of using the required pseudo-class. Here's what I did:

#reserved .mandatory-style {
    background: #eaeae6;
}

<input class="mandatory-style" type="email" id="email" name="email" pattern="[a-zA-Z0-9_]+([.][a-zA-Z0-9_]+)*@[a-zA-Z0-9_]+([.][a-zA-Z0-9_]+)*[.][a-zA-Z]{1,5}" style="width: 200px;" title="email" required/>

By making this adjustment, I successfully passed the W3C Validator! :)

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