:indeterminate

/* Selects any <input>, but only when its state is indeterminate  */
input:indeterminate {
  background: lime;
}

:indeterminate

input, span {
  background: red;
}

:indeterminate, :indeterminate + label {
  background: lime;
}

<div>
  <input type="checkbox" id="checkbox">
  <label for="checkbox">Background should be green</label>
</div>
<div>
  <input type="radio" id="radio">
  <label for="radio">Background should be green</label>
</div>

var inputs = document.getElementsByTagName("input"
for(var i = 0; i < inputs.length; i++) {
  inputs[i].indeterminate = true;
}

:indeterminate {
  opacity: 0.5;
}

<progress>