Hi

within the package manifest file you can add an additional "css" section

so the last example from the build your own editor page might become.

{
    "gridEditors": [
        {
            "name": "Code",
            "alias": "code",
            "view": "/app_plugins/yourpackage/editor.html",
            "icon": "icon-code",
            "config": {
                "color": "red",
                "text-align": "right"
            }
        }
    ],
    javascript:[
        "/app_plugins/yourpackage/editor.controller.js"
    ],
    css: [
        "/app_plugins/yourpackage/editorstyles.css"
    ]
}