How do I solve “Greetings, time traveller. We are in the golden age of prefix-less CSS, where Autoprefixer is no longer needed for your stylesheet.”?

Your issue can be solved package.json by applying code below:

 "browserslist": {
    "production": [
      ">0.3%",
      "not ie 11",
      "not dead", 
      "not op_mini all"
    ],
    "development": [
      "last 1 chrome version",
      "last 1 firefox version",
      "last 1 safari version",
      ">0.3%",
      "not ie 11",
      "not dead", 
      "not op_mini all"
    ]
  }

After you have made these changes restart your server. you will no longer get this warning.