title: Centering the title of an ioslides slide in RStudio
body: <p>I'm making a quick presentation in RStudio using a new Rmarkdown file, and I've set it to output an HTML file using <code>ioslides</code>. Here's what I've got:</p>
  
  <pre><code>---
  title: "SX MWE Presentation"
  author: "John Doe"
  date: "Today"
  output:
    ioslides_presentation:
      smaller: yes
      widescreen: yes
      transition: "faster" 
  ---
  
  ## Plan
  
  Here's the plan: I'm going to give one speech today and another next Monday. 
  
  ## Today's Speech 
  
  ## Today I'll be talking about A B and C. 
  
  ## Next Monday
  
  ## Next Monday I'll be talking about X Y and Z. 
  </code></pre>
  
  <p>Here's my question: I'd like to have the slide title text in <code>## Today's Speech</code> and <code>## Next Monday</code> slides be centered horizontally and vertically. How do I do that? You'll see immediately that these are just slides with no content, just a title, but that's intentional: I just want a couple of "setup" slides to anchor where we are. </p>
  
  <p>My suspicion is that, to center those slide titles on the slide, I need a custom css file of some kind, but I've been unable to find the code I think I'm looking for. (Of course, I've looked in the ioslides documentation for answer, but I didn't find one.) </p>