My chrome theme image does not fill the entire screen. What is wrong?

I'm creating a theme for Google Chrome, but the image does not fill the entire screen. I already consulted the documentation, read some tutorials, but my image does not fill the entire browser screen.

My manifest looks like this:

{
  "version": "2015.0.1",
  "description": "Nanatsu no Taizai Extension",
  "name": "Nanatsu no Taizai",

  "theme": {
    "images": {
      "theme_frame_overlay": "img/overlay-40.png",
      "theme_toolbar": "img/toolbar-120.png",
      "theme_ntp_background": "img/background.png",
      "theme_button_background": "img/button_30.png",
      "theme_tab_background": "img/tab.png"
    },
    "color": {
      "frame": [10, 17, 27],
      "toolbar": [10, 17, 27],
      "ntp_text": [255, 255, 255],
      "ntp_link": [255, 255, 255],
      "ntp_setion": [10, 17, 27],
      "button_background": [10, 17, 27]
    },
    "tints": {
      "buttons": [0.33, 0.5, 0.47]
    },
    "properties": {
      "ntp_background_alignment": "bottom",
      "ntp_background_repeat": "no-repeat"
    }
  },

  "author": "Josue",
  "manifest_version": 2

}

Below is the link to my browser's screensaver, with theme installed.

What's wrong with my manifest ?