The + selector in css means "immediate sibling", i.e. the very next element after the input must be a label. This will only select the immediate sibling.
An alternative is ~ which means "any sibling" and targets any label after the input.
In both of these cases, the elements (input and label) are on the same dom level. There is no way to traverse up the dom, grab the sibling and then the label - which is what you are trying to do with the html supplied.
If you are able to change the html, then either place the input outside the two divs or place both labels inside the same div (after the input).
.radioclass:checked ~ div label {
background-color: cyan;
}
<div class="row">
<input class="radioclass" id="id_radiobtn1" type="radio" name="radiobtn1" value="1">
<div class="col-sm-4">
<label for="id_radiobtn1">first label</label>
</div>
<div class="col-sm-4">
<label for="id_radiobtn1">second label</label>
</div>
</div>
.radioclass:checked ~ label {
background-color: cyan;
}
<div class="row">
<div class="col-sm-4">
<input class="radioclass" id="id_radiobtn1" type="radio" name="radiobtn1" value="1">
<label for="id_radiobtn1">first label</label>
<label for="id_radiobtn1">second label</label>
</div>
</div>
If you cannot alter the html, then JS is the only other approach (I've changed the input to a checkbox for demonstration purposes):
$('input').on('change', function(){
var func = 'removeClass';
if($(this).is(':checked')) {
func = 'addClass';
}
$('label[for="'+$(this).attr('id')+'"]')[func]('checked');
});
label.checked {
background-color: cyan;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<div class="row">
<div class="col-sm-4">
<input class="radioclass" id="id_radiobtn1" type="checkbox" name="radiobtn1" value="1">
<label for="id_radiobtn1">first label</label>
</div>
<div class="col-sm-4">
<label for="id_radiobtn1">second label</label>
</div>
</div>
:has()but its not yet supported by browsers.