layout.json

{
    "layout": {
        "type": "composite",
        "direction": "horizontal",
        "ratio": 1,
        "widgets": [
            {
                "type": "simple",
                "widget": "file_browser",
                "ratio": 1,
                "border": true
            },
            {
                "type": "composite",
                "direction": "vertical",
                "ratio": 1,
                "widgets": [
                    {
                        "type": "simple",
                        "widget": "music_player",
                        "ratio": 2,
                        "border": true
                    },
                    {
                        "type": "simple",
                        "widget": "playlist",
                        "ratio": 3,
                        "border": true
                    }
                ]
            }
        ]
    }
}