:default CSS pseudo-class

label,
input[type="submit"] {
  display: block;
  margin-top: 1em;
}

input:default {
  border: none;
  outline: 2px solid deeppink;
}

<form>
  <p>How did you find out about us?</p>
  <label><input name="origin" type="radio" value="google" checked=""> Google</label>
  <label><input name="origin" type="radio" value="facebook"> Facebook</label>
  <p>Please agree to our terms:</p>

  <label><input name="newsletter" type="checkbox" checked=""> I want to subscribe to
    a personalized newsletter.</label>

  <label><input name="privacy" type="checkbox"> I have read and I agree to the
    Privacy Policy.</label>

  <input type="submit" value="Submit form">
</form>

:default {
  /* ... */
}

<fieldset>
  <legend>Favorite season</legend>

  <input type="radio" name="season" id="spring" value="spring" />
  <label for="spring">Spring</label>

  <input type="radio" name="season" id="summer" value="summer" checked />
  <label for="summer">Summer</label>

  <input type="radio" name="season" id="fall" value="fall" />
  <label for="fall">Fall</label>

  <input type="radio" name="season" id="winter" value="winter" />
  <label for="winter">Winter</label>
</fieldset>

input:default {
  box-shadow: 0 0 2px 1px coral;
}

input:default + label {
  color: coral;
}