Markup: templates/output/04-elements/forms/errormessage/input-success.html
<div class="form-group form-success">
<div class="u-floating-label">
<input class="form-success" type="text" id="success-id" name="success-name" placeholder="Success"/>
<label for="success-id">Form success input field</label>
</div>
</div>
Source:
assets/sass/04-elements/_elements.forms.scss, line 802