:required
        
        
          
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      This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
The :required CSS pseudo-class represents any <input>, <select>, or <textarea> element that has the required attribute set on it.
Try it
label {
  display: block;
  margin-top: 1em;
}
.req {
  color: red;
}
*:required {
  background-color: gold;
}
<form>
  <label for="name">Name: <span class="req">*</span></label>
  <input id="name" name="name" type="text" required />
  <label for="birth">Date of Birth:</label>
  <input id="birth" name="birth" type="date" />
  <label for="origin"
    >How did you find out about us? <span class="req">*</span></label
  >
  <select id="origin" name="origin" required>
    <option>Google</option>
    <option>Facebook</option>
    <option>Advertisement</option>
  </select>
  <p><span class="req">*</span> - Required field</p>
</form>
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 {
  /* ... */
}
Accessibility
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.
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: maroon;
  border-width: 3px;
}
input:required:invalid {
  border-color: #c00000;
}
Result
Specifications
| Specification | 
|---|
| HTML> # selector-required>  | 
            
| Selectors Level 4> # required-pseudo>  | 
            
Browser compatibility
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See also
- Other validation-related pseudo-classes: 
:optional,:invalid,:valid - Form data validation