How to use the lookatme.schemas.HeadingsSchema function in lookatme

"bg": "default",
    })
    author = fields.Nested(StyleFieldSchema, default={
        "fg": "#f30",
        "bg": "default",
    })
    date = fields.Nested(StyleFieldSchema, default={
        "fg": "#777",
        "bg": "default",
    })
    slides = fields.Nested(StyleFieldSchema, default={
        "fg": "#f30",
        "bg": "default",
    })

    headings = fields.Nested(HeadingsSchema, default=HeadingsSchema().dump(HeadingsSchema()))
    bullets = fields.Nested(BulletsSchema, default=BulletsSchema().dump(BulletsSchema()))
    table = fields.Nested(TableSchema, default=TableSchema().dump(TableSchema()))
    quote = fields.Nested(BlockQuoteSchema, default=BlockQuoteSchema().dump(BlockQuoteSchema()))
    link = fields.Nested(StyleFieldSchema, default={
        "fg": "#33c,underline",
        "bg": "default",
    })


class MetaSchema(Schema):
    """The schema for presentation metadata
    """
    class Meta:
        render_module = YamlRender

    title = fields.Str(default="", missing="")