title: Change Mermaid theme in markdown
body: <p>I use mermaid for basic diagram rendering within my markdown documentation aside my code. I found <a href="https://mermaidjs.github.io/mermaid-live-editor/" rel="noreferrer">this online editor</a> useful to edit this while having a preview. This proposes to change theme (<em>default</em> and <em>forest</em> works).</p>
  
  <p>How can I set theme when I copy paste this into my markdown document ? </p>