:default CSS pseudo-class

label {
  display: block;
  margin-top: 0.5em;
}

fieldset {
  margin-top: 0.5em;
}

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

<label for="name">Name (required):</label>
<input id="name" name="name" type="text" required />

<label for="birth">Date of birth:</label>
<input id="birth" name="birth" type="date" />

<label for="origin">How did you find out about us? (required)</label>
<select id="origin" name="origin" required>
  <option value="">Choose an option</option>
  <option value="google">Google</option>
  <option value="facebook">Facebook</option>
  <option value="advertisement">Advertisement</option>
</select>

<fieldset>
  <legend>Preferred contact method:</legend>
  <label>
    <input name="contact" type="radio" value="email" checked /> Email
  </label>
  <label><input name="contact" type="radio" value="phone" /> Phone</label>
</fieldset>

<label>
  <input name="newsletter" type="checkbox" checked /> I want to subscribe to a
  personalized newsletter.
</label>
<label>
  <input name="privacy" type="checkbox" required /> I have read and I agree to
  the Privacy Policy (required).
</label>

: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;
}