Adding width and height options in config.json of Rendertron does not change dimension of rendered page

Question

I want rendertron to render pages of particular dimensions. According to the documentation (https://github.com/GoogleChrome/rendertron#config), I added the width and height properties to my config.json file:

  "width": 480,
  "height": 600,
  "cache": "memory",
  "cacheConfig": {
    "cacheDurationMinutes": 120,
    "cacheMaxEntries": 100
  },
  "closeBrowser": true,
  "port": 3002
}

However, this does not seem to work and rendertron is still using the default value which is 1000x1000. Has someone faced this issue?

This is what one of the rendered page looks like: