CSS :checked Selector - Styling Checkboxes and Radios

The :checked Pseudo-class

The :checked selector matches form elements that are currently checked or selected: checkboxes, radio buttons, and <option> elements.

Basic Usage

input[type="checkbox"]:checked {
  accent-color: #3b82f6;
}

input[type="radio"]:checked + label {
  font-weight: bold;
  color: #3b82f6;
}

Custom Checkbox

/* Hide native checkbox */
input[type="checkbox"] {
  appearance: none;
  width: 20px;
  height: 20px;
  border: 2px solid #ccc;
  border-radius: 4px;
  cursor: pointer;
}

input[type="checkbox"]:checked {
  background: #3b82f6;
  border-color: #3b82f6;
  background-image: url("data:image/svg+xml,...");
}

CSS-Only Toggle Switch

<label class="switch">
  <input type="checkbox" />
  <span class="slider"></span>
</label>

.switch input:checked + .slider {
  background-color: #3b82f6;
}

.switch input:checked + .slider::before {
  transform: translateX(24px);
}

CSS-Only Accordion

The checkbox hack enables interactive components without JavaScript:

<input type="checkbox" id="section1" hidden />
<label for="section1">Section Title</label>
<div class="content">Content here...</div>

.content {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.3s;
}

input:checked ~ .content {
  max-height: 500px;
}

The :indeterminate State

Checkboxes can have an indeterminate state (set via JavaScript) that represents a partial or unknown selection:

input:indeterminate + label {
  color: #999;
  font-style: italic;
}

Specificity

:checked has specificity (0, 1, 0) — same as a class selector.