How can CSS be used to style hidden fields in PHP forms?

To style hidden fields in PHP forms using CSS, you can assign a class or ID to the hidden field and then apply styles to that class or ID in your CSS file. This allows you to customize the appearance of hidden fields to match the design of your form.

<input type="hidden" name="hidden_field" id="hidden_field" class="hidden-field">
```

```css
.hidden-field {
    display: none;
}