I am trying to use colorbar for an output variable circle plot in Folium

colormap = cm.LinearColormap(colors=['green','red'], index=[min(df['output']), max(df['output'])], vmin=min(df['output']),vmax=max(df['output']), caption='output in units')

folium.Circle(location=[row['Latitude'], row['Longitude']], 
                        radius=800*row["output"],
                        fill=True,
                        # opacity=0.8,
                        # fill_opacity=1,
                        color=colormap(row["output"])).add_to(m)

When I use this code, the caption text “output in units” is appearing very small. I want to increase its font size. Please suggest any possible solutions