Styler lets you inject .css and .js files into web sites you visit

1. Pull this repository
2. Navigate to chrome://extensions
3. Make sure that the Developer mode checkbox in the top right corner is checked
4. Click on the Load unpacked extension ... button and select the folder where you downloaded this repository

{
  "github": {
    "enabled": true,
    "domains": [
      "github.com",
      "gist.github.com"
    ],
    "inject": {
      "css": [
        "github-general-fixes.css",
        "github-dark.css",
        "github-pygments.css"
      ]
    }
  },

  "youtube": {
    "enabled": true,
    "domains": [
      "www.youtube.com"
    ],
    "inject": {
      "css": ["youtube.css"],
      "js": ["some.js"]
    }
  }
}

sites/
├── config.json
├── github
│   ├── github-dark.css
│   ├── github-general-fixes.css
│   └── github-pygments.css
└── youtube
    ├── some.js
    └── youtube.css

1. Create a folder called sites under the root folder of this extension
2. Copy the above configuration in sites/config.json
3. Create two separate directories: sites/github and sites/youtube, and place your styles and scripts there
4. Each time you make changes to the configuration or the styles, you have to click the Reload (Ctrl+R) link of the Styler extension under chrome://extensions