Up to this point, I had my diagram in a regular markdown file. The problem is when the diagram got bigger, the previewer can't zoom in. Reading the extension doc, it does support pan and zoom. However, I wasn't able to access that feature.

After playing around a little, I figured out the way to do it. The previewer supports only .mmd file. So, here are the steps I did:

1. Move mermaid diagram to mmd file.
2. Open the mmd file in VS code.
3. Click CTRL + Shift + P and search for MermaidChart: PreviewDiagram

By default, it has no key binding, so I bind mine to ALT + SHIFT + M for quick access.