settings.json

"editor.tokenColorCustomizations": {
  "textMateRules": [
    {
      "scope": [
        //following will be in italic (=FlottFlott)
        "comment",
        "entity.name.type.class", //class names
        "keyword", //import, export, return…
        "constant", //String, Number, Boolean…, this, super
        "storage.modifier", //static keyword
        "storage.type.class.js", //class keyword
      ],
      "settings": {
        "fontStyle": "italic"
      }
    },
    {
      "scope": [
        //following will be excluded from italics (VSCode has some defaults for italics)
        "invalid",
        "keyword.operator",
        "constant.numeric.css",
        "keyword.other.unit.px.css",
        "constant.numeric.decimal.js",
        "constant.numeric.json"
      ],
      "settings": {
        "fontStyle": ""
      }
    }
  ]
}