:required - CSS: Cascading Style Sheets 编辑

The :required CSS pseudo-class represents any <input>, <select>, or <textarea> element that has the required attribute set on it.

/* Selects any required <input> */
input:required {
  border: 1px dashed red;
}

This pseudo-class is useful for highlighting fields that must have valid data before a form can be submitted.

Note: The :optional pseudo-class selects optional form fields.

Syntax

:required

Examples

The required field has a red border

HTML

<form>
  <div class="field">
    <label for="url_input">Enter a URL:</label>
    <input type="url" id="url_input">
  </div>

  <div class="field">
    <label for="email_input">Enter an email address:</label>
    <input type="email" id="email_input" required>
  </div>
</form>

CSS

label {
  display: block;
  margin: 1px;
  padding: 1px;
}

.field {
  margin: 1px;
  padding: 1px;
}

input:required {
  border-color: #800000;
  border-width: 3px;
}

input:required:invalid {
  border-color: #c00000;
}

Result

Accessibility concerns

Mandatory <input>s should have the required attribute applied to them. This will ensure that people navigating with the aid of assistive technology such as a screen reader will be able to understand which inputs need valid content to ensure a successful submission.

If the form also contains optional inputs, required inputs should be indicated visually using a treatment that does not rely solely on color to convey meaning. Typically, descriptive text and/or an icon are used.

• MDN Understanding WCAG, Guideline 3.3 explanations
• Understanding Success Criterion 3.3.2 | W3C Understanding WCAG 2.0

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• Other validation-related pseudo-classes: :optional, :invalid, :valid
• Form data validation