The :optional CSS pseudo-class selects any <input> or <textarea> element that does not have the required attribute set on it. This allows forms to easily indicate optional fields, and to style them accordingly.
/* Selects <input> elements, but only if they are */
/* optional, i.e. have not got required set on them */
input:optional {
  border: 1px dashed black;
}
To provide styling for required form fields, the :required pseudo-class may be used.
Syntax
:optional
Examples
See :invalid for examples.
Specifications
| Specification | Status | Comment | 
|---|---|---|
| WHATWG HTML Living Standard The definition of ':optional' in that specification. | Living Standard | No change. | 
| HTML5 The definition of ':optional' in that specification. | Recommendation | Defines the semantic regarding HTML and constraint validation. | 
| Selectors Level 4 The definition of ':optional' in that specification. | Working Draft | No change. | 
| CSS Basic User Interface Module Level 3 The definition of ':optional' in that specification. | Candidate Recommendation | Defines the pseudo-class, but not the associated semantic. | 
Browser compatibility
| Feature | Chrome | Edge | Firefox (Gecko) | Internet Explorer | Opera | Safari | 
|---|---|---|---|---|---|---|
| Basic support | 10.0 | (Yes) | 4.0 (2) | 10 | 10.0 | 5.0 | 
| Feature | Android | Edge | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile | 
|---|---|---|---|---|---|---|
| Basic support | 4.4 | (Yes) | 4.0 (2) | No support | 10.0 | 5.0 | 
See also
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                       Last updated by:
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