This is the code, I've tried different attribute selectors with no avail. It important that the element is inside a div since it simulates the structure in the real website.
#AAA:checked ~ #BBB {
color:red;
}
<div>
<input type="radio" id="#AAA">click
</div>
<div id="CCC">some content</div>
<div id="BBB">some content</div>