A very important built-in package for creating responsive layouts is the alexa-layouts package. You import this package into the APL document as shown in the example below.

    "type": "APL",
    "version": "1.7",
    "theme": "dark",
    "import": [
            "name": "alexa-layouts",
            "version": "1.4.0"
    "mainTemplate": {
        "items": []

APL is a declarative language, so the order of the top-level document properties doesn't matter most of the time. You just need to maintain a logical structure.