message: add build:css run-script; run it prestart
diff: "scripts": {
  "prebuild": "rm -rf dist",
  "build": "NODE_ENV=production rollup -c",
  + "build:css": "script/build-css > docs/system.css",
  "build:docs": "x0 build examples --out-dir docs",
  "lint": "eslint src examples",
  "prepublishOnly": "npm run build",
  + "prestart": "npm run build:css",
  "start": "x0 dev examples -op 8888",
  "test": "jest",
  "watch": "jest --watch --no-coverage"
  