:checked

label,
input[type="submit"] {
 display: block;
 margin-top: 1em;
}
input:checked {
 border: none;
 outline: 2px solid deeppink;
}

<form>
 <p>How did you find out about us?</p>
 <label
 ><input name="origin" type="radio" value="google" checked /> Google</label
 >
 <label><input name="origin" type="radio" value="facebook" /> Facebook</label>
 <p>Please agree to our terms:</p>
 <label
 ><input name="newsletter" type="checkbox" checked /> I want to subscribe to
 a personalized newsletter.</label
 >
 <label
 ><input name="privacy" type="checkbox" /> I have read and I agree to the
 Privacy Policy.</label
 >
 <input type="submit" value="Submit form" />
</form>

Hinweis: Da Browser <option>s häufig als ersetzte Elemente behandeln, variiert der Umfang, in dem sie mit der :checked Pseudoklasse gestylt werden können, von Browser zu Browser. Die Funktionalität des anpassbaren Auswahlelements kann verwendet werden, um in unterstützenden Browsern eine vollständige Anpassung von <option>-Elementen wie bei jedem regulären DOM-Element zu ermöglichen.

:checked {
 /* ... */
}

<div>
 <input type="radio" name="my-input" id="yes" value="yes" />
 <label for="yes">Yes</label>
 <input type="radio" name="my-input" id="no" value="no" />
 <label for="no">No</label>
</div>
<div>
 <input type="checkbox" name="my-checkbox" id="opt-in" />
 <label for="opt-in">Check me!</label>
</div>
<select name="my-select" id="fruit">
 <option value="opt1">Apples</option>
 <option value="opt2">Grapes</option>
 <option value="opt3">Pears</option>
</select>

div,
select {
 margin: 8px;
}
/* Labels for checked inputs */
input:checked + label {
 color: red;
}
/* Radio element, when checked */
input[type="radio"]:checked {
 box-shadow: 0 0 0 3px orange;
}
/* Checkbox element, when checked */
input[type="checkbox"]:checked {
 box-shadow: 0 0 0 3px hotpink;
}
/* Option elements, when selected */
option:checked {
 box-shadow: 0 0 0 3px lime;
 color: red;
}

<input type="checkbox" id="expand-toggle" />
<table>
 <thead>
 <tr>
 <th>Column #1</th>
 <th>Column #2</th>
 <th>Column #3</th>
 </tr>
 </thead>
 <tbody>
 <tr class="expandable">
 <td>[more text]</td>
 <td>[more text]</td>
 <td>[more text]</td>
 </tr>
 <tr>
 <td>[cell text]</td>
 <td>[cell text]</td>
 <td>[cell text]</td>
 </tr>
 <tr>
 <td>[cell text]</td>
 <td>[cell text]</td>
 <td>[cell text]</td>
 </tr>
 <tr class="expandable">
 <td>[more text]</td>
 <td>[more text]</td>
 <td>[more text]</td>
 </tr>
 <tr class="expandable">
 <td>[more text]</td>
 <td>[more text]</td>
 <td>[more text]</td>
 </tr>
 </tbody>
</table>
<label for="expand-toggle" id="expand-btn">Toggle hidden rows</label>

/* Hide the toggle checkbox */
#expand-toggle {
 display: none;
}
/* Hide expandable content by default */
.expandable {
 visibility: collapse;
 background: #dddddd;
}
/* Style the button */
#expand-btn {
 display: inline-block;
 margin-top: 12px;
 padding: 5px 11px;
 background-color: #ffff77;
 border: 1px solid;
 border-radius: 3px;
}
/* Show hidden content when the checkbox is checked */
#expand-toggle:checked ~ * .expandable {
 visibility: visible;
}
/* Style the button when the checkbox is checked */
#expand-toggle:checked ~ #expand-btn {
 background-color: #cccccc;
}

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