:indeterminate CSS pseudo-class

:indeterminate {
  /* ... */
}

<fieldset>
  <legend>Checkbox</legend>
  <div>
    <input type="checkbox" id="checkbox" />
    <label for="checkbox">This checkbox label starts out lime.</label>
  </div>
</fieldset>

<fieldset>
  <legend>Radio</legend>
  <div>
    <input type="radio" id="radio1" name="radioButton" value="val1" />
    <label for="radio1">First radio label starts out lime.</label>
  </div>
  <div>
    <input type="radio" id="radio2" name="radioButton" value="val2" />
    <label for="radio2">Second radio label also starts out lime.</label>
  </div>
</fieldset>

input:indeterminate + label {
  background: lime;
}

fieldset {
  padding: 1em 0.75em;
}

fieldset:first-of-type {
  margin-bottom: 1.5rem;
}

fieldset:not(:first-of-type) > div:not(:last-child) {
  margin-bottom: 0.5rem;
}

const inputs = document.getElementsByTagName("input");

for (const input of inputs) {
  input.indeterminate = true;
}

<progress></progress>

progress {
  margin: 4px;
}

progress:indeterminate {
  width: 80vw;
  height: 20px;
}