title: Select theme in Revealjs from pandoc
body: <p>When I run below command to generate slides from markdown, the theme not selected correctly.</p>
  
  <pre><code>pandoc slides -o slides.html -s -V theme=beige -t revealjs
  </code></pre>
  
  <p>My slide is in a directory with reveal.js there:</p>
  
  <pre><code>|-- reveal.js
  |   |-- css
  |   |   |-- reveal.min.css
  |   |   `-- theme
  |   |       |-- beige.css
  |   |-- js
  |   |   |-- reveal.js
  |   |   `-- reveal.min.js
  |   `-- lib
  |       |-- css
  |       |   `-- zenburn.css
  |       `-- js
  |           |-- classList.js
  `-- slides.md
  </code></pre>
  
  <p>But it seems it still not use the theme.</p>