Example of maxWidth and maxHeight in Flex Message

maxWidthHeight.json

{
  "type": "bubble",
  "body": {
    "type": "box",
    "layout": "vertical",
    "contents": [
      {
        "type": "box",
        "layout": "horizontal",
        "contents": [
          {
            "type": "button",
            "action": {
              "type": "message",
              "label": "maxWidth 75%",
              "text": " "
            },
            "style": "primary"
          }
        ],
        "maxWidth": "75%"
      },
      {
        "type": "box",
        "layout": "horizontal",
        "contents": [
          {
            "type": "button",
            "style": "secondary",
            "action": {
              "type": "message",
              "label": "maxHeight 40px",
              "text": " "
            }
          }
        ],
        "maxHeight": "40px"
      }
    ],
    "spacing": "xl"
  }
}