Unfortunately, this is a job for Javascript, but I can get you part of the way using Pure CSS using variables.. but this is obviously no better than having hidden divs.
:root {
--active-contentA: 'A';
--active-contentB: 'B';
}
input[data-value='A']:checked ~ #value::after {
color: red;
content: var(--active-contentA);
}
input[data-value='B']:checked ~ #value::after {
color: red;
content: var(--active-contentB);
}
<label for="checkbox1">checkbox1</label>
<input type="radio" name="check" id="checkbox1" data-value="A">
<label for="checkbox2">checkbox2</label>
<input type="radio" name="check" id="checkbox2" data-value="B">
<h1 id="value">
Letters:
</h1>
See JSFiddle
This is the Javascript solution:
document.addEventListener('input', function (evt) {
var data = evt.target.getAttribute('data-value');
var value = document.getElementById('value');
value.innerHTML = "Letters: " + data;
});
<label for="checkbox1">checkbox1</label>
<input type="radio" name="check" id="checkbox1" data-value="A">
<label for="checkbox2">checkbox2</label>
<input type="radio" name="check" id="checkbox2" data-value="B">
<h1 id="value">
Letters:
</h1>
See JSFiddle
Goodluck!