title: How to target a Div in CSS in Rmarkdown HTML
body: <p><a href="https://i.stack.imgur.com/WEnqI.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/WEnqI.png" alt="enter image description here" /></a></p>
  <p>I'd like to be able to control the header of this HTML file with CSS inside Rmarkdown. I want to change the text size, but can't seem to control it, here is what I have tried</p>
  <pre><code>div.header.fluid-row {
    font-size: 12;
  }
  
  div.fluid-row {
    font-size: 12;
  }
  </code></pre>