Markup: templates/output/04-elements/forms/input/datetime.html
<div class="flex__12 powermail_fieldwrap">
<label for="demoformid-idt">Birthday (date and time)</label>
<input class="" type="datetime" name="" id="demoformid-idt" value="1970-01-01T00:00:00Z"/>
</div>
<div class="flex__12 powermail_fieldwrap">
<label for="demoformid-idt-error">Birthday (date and time)</label>
<input class="" type="datetime" name="" id="demoformid-idt-error" value="1970-01-01T00:00:00Z"/>
<ul class="powermail-errors-list">
<li>This field is required</li>
</ul>
</div>
Source:
assets/sass/04-elements/_elements.forms.scss, line 227