VulcanBoard/vulcanboard.kv

<ErrorPopup@Popup>:
    message: message
    auto_dismiss: False
    title: "Error"
    size_hint: None, None
    width: grid.width + dp(25)
    height: grid.height + root.title_size + dp(48)

    GridLayout:
        id: grid
        size_hint: None, None
        size: self.minimum_size
        padding: [10, 5]
        cols: 1
        AnchorLayout:
            anchor_x: "center"
            anchor_y: "bottom"
            size_hint: None, None
            height: message.height
            width: max(message.width, butt.width)
            Label:
                id: message
                size_hint: None, None
                size: self.texture_size
                padding: [10, 5]
        AnchorLayout:
            anchor_x: "center"
            anchor_y: "bottom"
            size_hint: None, None
            height: butt.height
            width: max(message.width, butt.width)
            Button:
                id: butt
                text: 'Close'
                size_hint: None, None
                size: self.texture_size
                padding: [10, 5]
                on_release: root.error_exit();