What option is needed for the chart (Google Charts)?

Question

Google

I need an Area Chart with filling below it, but the lines there are such that the derivative does not exist in them (sharp corners), and I need the derivative to be equal to 0, that is, as in the Line Chart (rounded corners), what property is there can be used? There is "Configuration Options" down there, but they are in English and I do not know what is needed for me. Thank you for your responses!