db9.py

row1 = dbc.Row(dbc.Col(html.Div("A single column")))

row2 = dbc.Row(
            [
                dbc.Col(html.Div("One of three columns")),
                dbc.Col(html.Div("One of three columns")),
                dbc.Col(html.Div("One of three columns")),
            ]
        )
import dash_bootstrap_components as dbc
from dash import html

app = JupyterDash(__name__, external_stylesheets = [dbc.themes.BOOTSTRAP])

app.layout =  html.Div(
    [
        row1,
        row2
    ] 
)

app.run_server()
Dash app running on http://127.0.0.1:8050/