less - On input focus change color of label. How?

Question

On input focus I want to change the color of the label element. How can I achieve this in less?

.control-label{
      color: @gray-light;
}
.controls{
  input,
  textarea{
    background-color:red; 
    &:focus{
      .control-label &{
        color: red;  //HERE
      }

    }
}

HTML:

<div class="control-group">
    <label class="control-label" for="inputEmail">Firstname</label>
    <div class="controls">
        <input type="text" id="inputEmail" placeholder="Firstname">
    </div>
</div>

Answer 1

I don't think you can without changing your HTML, see also: Is there any way to hover over one element and affect a different element?, your elements should be direct siblings. (LESS don't help to solve your problem here, LESS generate CSS and it seems impossible to do in CSS)

Possible suggestion:

input:focus + .control-label
{
    background-color:purple;
    color: red;
}
.controls > input
{
    float:right;
}

<div class="controls">
    <input type="text" id="inputEmail" placeholder="Firstname">
    <label class="control-label" for="inputEmail">Firstname</label>
</div>