vsc-material-theme/icons/material-theme-icon-theme.json

{
  "iconDefinitions": {
    "_markdown": {
      "iconPath": "svg/markdown.svg"
    },
    "_sass": {
      "iconPath": "svg/sass.svg"
    },
    "_scss": {
      "iconPath": "svg/scss.svg"
    },
    "_json": {
      "iconPath": "svg/json.svg"
    }
  },
  "fileExtensions": {
    "md": "_markdown",
    "scss": "_scss",
    "sass": "_sass",
    "json": "_json"
  }
}