Markup: templates/output/04-elements/forms/input/checkbox.html
<form class="powermail_form" action="#" method="post">
<div class="powermail_fields">
<div class="powermail_fieldwrap powermail_fieldwrap_type_check">
<div class="powermail_field ">
<div class="checkbox">
<input class="powermail_checkbox" type="checkbox" id="checkboxdemo-a" name="checkboxdemo-a" checked="checked"/>
<label for="checkboxdemo-a"><span class="powermail_checkbox_label">Newsletter</span><span>Send me the newsletter once a month.</span>
</label>
</div>
</div>
</div>
<div class="powermail_fieldwrap powermail_fieldwrap_type_check">
<div class="powermail_field ">
<div class="checkbox">
<input class="powermail_checkbox" type="checkbox" id="checkboxdemo-hide-label" name="checkboxdemo-hide-label"/>
<label for="checkboxdemo-hide-label"><span class="powermail_checkbox_label u-visually-hidden">Newsletter</span><span>Send me the newsletter once a month.</span>
</label>
</div>
</div>
</div>
<div class="powermail_fieldwrap powermail_fieldwrap_type_check">
<div class="powermail_field ">
<div class="checkbox">
<input class="powermail_checkbox" type="checkbox" id="checkboxdemo-b" name="checkboxdemo-b"/>
<label for="checkboxdemo-b"><span class="powermail_checkbox_label">Declaration of consent<span class="mandatory" aria-hidden="true">*</span><span class="u-visually-hidden"> Required field</span></span><span>I have read the <a href="#">declaration of consent</a>.</span>
</label>
</div>
</div>
<p class="powermail_field_description" id="checkboxdemo-b-description">Without your consent we cannot process your request.</p>
</div>
<div class="powermail_fieldwrap powermail_fieldwrap_type_check">
<div class="powermail_field ">
<div class="checkbox powermail_field_error">
<input class="powermail_checkbox" type="checkbox" id="checkboxdemo-error" name="checkboxdemo-error"/>
<label for="checkboxdemo-error"><span class="powermail_checkbox_label">Declaration of consent<span class="mandatory" aria-hidden="true">*</span><span class="u-visually-hidden"> Required field</span></span><span>I have read the <a href="#">declaration of consent</a>.</span>
</label>
</div>
<ul class="powermail-errors-list filled" aria-live="polite">
<li>This field is required</li>
</ul>
</div>
</div>
</div>
</form>
Source:
assets/sass/04-elements/_elements.forms.scss, line 208