<label>
  <input type="radio" name="a">
  <span>Показать блок 1</span>
  <div>block 1</div>
</label>

<label>
  <input type="radio" name="a">
  <span>Показать блок 2</span>
  <div>block 2</div>
</label>

<label>
  <input type="radio" name="a">
  <span>Показать блок 3</span>
  <div>block 3</div>
</label>
label input,
label div {
  display: none;
}
label {
  display: block;
}

input:checked ~ div {
  display: block;
}

External CSS

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External JavaScript

This Pen doesn't use any external JavaScript resources.