Change mermaid theme preview on VSCode

Question

I use mermaid for make diagrams in basic markdown documents and I want to change the default theme to the neutral theme. I use VSCode and Markdown enhanced preview extension. I tried to change the mermaid_config.js file adding "theme": "neutral". Not works.

// config mermaid init call
// http://knsv.github.io/mermaid/#configuration
//
// You can edit the 'MERMAID_CONFIG' variable below.
MERMAID_CONFIG = {
  startOnLoad: false,
  "theme": "neutral"
}