discourse/app/assets/javascripts/admin/templates/customize-email-templates-edit.hbs

<div class='email-template'>
  <label>
    {{i18n "admin.customize.email_templates.subject"}}
    {{input value=buffered.subject}}
  </label>

  <label>
    {{i18n "admin.customize.email_templates.body"}}
    {{d-editor value=buffered.body}}
  </label>

  {{#save-controls model=emailTemplate action="saveChanges" saved=saved}}
    {{#if emailTemplate.can_revert}}
      {{d-button action="revertChanges" label="admin.customize.email_templates.revert"}}
    {{/if}}
  {{/save-controls}}
</div>