How to add border radius?

Pro version

1
Border radius for the whole slider

Be sure to switch to Expert mode first. Then go to the Slider settings → General tab → under Simple slider type settings and locate the Border setting. Set the border radius to the value you would like to have, then write

overflow: hidden;

to the Slider → CSS field.

2
Border radius for specific edges

In Expert mode locate the Slider settings → General tab → under Simple slider type settings → Slider: CSS. You can write here the codes to achieve the desired Border radius effect.

Don't forget to write overflow: hidden; as well.