title: How to change table header color in BootstraVue b-table
body: <p>I would like to change the color of b-table in BootstraVue b-table component.
  The simple example is:</p>
  
  <pre><code>&lt;template&gt;
      &lt;div&gt;
          &lt;b-table :items="items" thead-class="greenColor"&gt;
          &lt;/b-table&gt;
      &lt;/div&gt;
  &lt;/template&gt;
  &lt;style scoped&gt;
  .greenColor, .table thead th, thead, th {
      background-color: #00FF00 !important;
  }
  &lt;/style&gt;
  &lt;script&gt;
  export default {
      data() {
          return {
              items: [
                  {name: "Paweł", surname: "Kowalski"},
                  {name: "John", surname: "Nowak"}
              ]
          }
      }
  }
  &lt;/script&gt;
  </code></pre>
  
  <p>As you see I tried to set thead-class (and class sets correctly but doesn't work) and change style of thead element but the table is still white.
  Do you the way that I can change the color of this header?</p>
  
  <p>And some of my dependencies from <em>package.json</em>:
      "nuxt": "^2.0.0",
      "bootstrap": "^4.1.3",
      "bootstrap-vue": "^2.0.0"</p>