{% load i18n %}
<div class="btn-group">
  <a href="#" id="save-order" class="btn btn-primary btn-sm" style="display: None" post-url="{{ save_order_url }}">
      {% trans "Save Order" %}
  </a>
</div>

{% load i18n %}
<div class="btn-group">
  <a href="#" id="save-order" class="btn btn-success btn-sm" style="display: None" post-url="{{ save_order_url }}">
      <i class="fa fa-save">&nbsp;</i>{% trans "Save Order" %}
  </a>
</div>

Add icon sotablelist; Change buttom theme.
Add icon sotablelist; Change buttom theme.
