html.Fieldset border not showing

Hello guys, I have the following HTML content in my application:

html.Fieldset(
    id='smoothness-fieldset',
    style={'border-style': 'solid'},
    children=[
        html.Legend(children='Smoothness'),
        dbc.Row(
            children=[
                dbc.Col(
                    width=3,
                    children=dbc.Label('Size', html_for='smooth-slider')
                ),
                dbc.Col(
                    children=[
                        dcc.Slider(
                            id='smooth-slider',
                            min=1,
                            max=4,
                            step=1,
                            value=3,
                            marks=dict([(n, n) for n in range(1, 5)])
                        )
                    ]
                )
            ]
        )
    ]
)

Well, Fieldset is shown with no border at all. How could I fix it?

For all people seeking through this, try :

'borderStyle':'solid'