The checked selector is used to select all checked elements in the input tag and radio buttons. This selector is used with radio buttons, checkbox and option elements.
Syntax:
:checked {
// CSS property
}
Example 1: In this example, The CSS :checked selector targets checked input elements. It sets a height and width for checked checkboxes and applies a green color to the h1 element.
html
<!DOCTYPE html>
<html>
<head>
<title>
checked selector property
</title>
<style>
h1 {
color: green;
}
input:checked {
height: 8px;
width: 10px;
}
body {
width: 60%;
}
</style>
</head>
<body>
<h1>GeeksforGeeks</h1>
<h2>:checked Selector</h2>
<form action="">
Gender:
<input type="radio"
checked="checked"
value="male"
name="gender">
Male
<input type="radio"
value="female"
name="gender">
Female<br><br>
Computer Science Subjects:<br>
<input type="checkbox"
checked="checked"
value="Bike">
Computer Network<br>
<input type="checkbox"
checked="checked"
value="Bike">
Operating System<br>
<input type="checkbox"
value="Bike">
Mathematics<br>
<input type="checkbox"
value="Bike">
Physics<br>
</form>
</body>
</html>
Output: 
Example 2: In this example, The CSS option:checked selector targets the selected option within a <select> element. It sets a height of 10px and a font size of 20px for the selected option.
html
<!DOCTYPE html>
<html>
<head>
<title>checked selector</title>
<style>
option:checked {
height: 10px;
font-size: 20px;
}
h1 {
color: green;
}
</style>
</head>
<body>
<center>
<h1>GeeksForGeeks</h1>
<h2>:checked Selector in <option> Element</h2>
<select>
<option value="DataStructure">
Data Structure
</option>
<option value="Computer Network">
Computer Network
</option>
<option value="Operating System">
Operating System
</option>
<option value="Computer Architecture">
Computer Architecture
</option>
</select>
</center>
</body>
</html>
Output: 
Supported Browsers: The browser supported by :checked Selector are listed below:
- Apple Safari 3.1 and above
- Google Chrome 1.0 and above
- Edge 12.0 and above
- Firefox 1.0 and above
- Opera 9.0 and above