The eventBorderRadius property (number or string) applies the specified border radius to events and drag-and-drop shadows via inline styles in the JavaScript Monthly Calendar.
The value should be a string in the CSS format for the border-radius style. If the value is a number (e.g. 15) it will be applied as a pixel value ("15px").
It lets you override the CSS defined in the CSS theme.
You can also set the border radius for individual events using the onBeforeEventRender event handler (args.data.borderRadius).
nullCalendar config:
{
eventBorderRadius: "25px",
// ...
}