discourse/app/assets/javascripts/admin/addon/components/email-styles-editor.hbs

<div class="row">
  <div class="admin-controls">
    <nav>
      <ul class="nav nav-pills">
        <li>
          <LinkTo
            @route="adminCustomizeEmailStyle.edit"
            @model="html"
            @replace={{true}}
          >
            {{i18n "admin.customize.email_style.html"}}
          </LinkTo>
        </li>
        <li>
          <LinkTo
            @route="adminCustomizeEmailStyle.edit"
            @model="css"
            @replace={{true}}
          >
            {{i18n "admin.customize.email_style.css"}}
          </LinkTo>
        </li>
      </ul>
    </nav>
  </div>
</div>

<AceEditor
  @content={{this.editorContents}}
  @onChange={{fn (mut this.editorContents)}}
  @mode={{this.currentEditorMode}}
  @editorId={{this.editorId}}
  @save={{@save}}
/>

<div class="admin-footer">
  <div class="buttons">
    <DButton
      @action={{this.reset}}
      @disabled={{this.resetDisabled}}
      @label="admin.customize.email_style.reset"
      class="btn-default"
    />
  </div>
</div>