title: How to change header of bootstrap4 django-tables2
body: <p>I defined the table as below</p>
  
  <pre><code>class MyTable(tables.Table):
      class Meta:
          template_name = "django_tables2/bootstrap4.html"
          model = Mymodel
          attrs = {"class": "table table-hover"}
  </code></pre>
  
  <p>I want to change the table head to make  appear light or dark gray, <a href="https://getbootstrap.com/docs/4.0/content/tables/#table-head-options" rel="nofollow noreferrer">like this</a>. </p>