Markup: templates/output/04-elements/forms/input/datetime-local.html
<div class="flex__12 powermail_fieldwrap">
<label for="demoformid-idtl">Birthday (date and time)</label>
<input class="" type="datetime-local" name="" id="demoformid-idtl" value="1970-01-01T00:00"/>
</div>
<div class="flex__12 powermail_fieldwrap">
<label for="demoformid-idtl-error">Birthday (date and time)</label>
<input class="" type="datetime-local" name="" id="demoformid-idtl-error" value="1970-01-01T00:00"/>
<ul class="powermail-errors-list">
<li>This field is required</li>
</ul>
</div>
Source:
assets/sass/04-elements/_elements.forms.scss, line 239