gatsby-remark-classes.js

{
    resolve: `gatsby-transformer-remark`,
    options: {
      plugins: [
        {
          resolve: `gatsby-remark-classes`,
          options: {
            classMap: {
              "heading[depth=1]": "text-2xl",
              "heading[depth=2]": "text-xl",
              "paragraph": "text-base"
            }
          }
        }
      ]
    }
  }