The border-spacing property in CSS controls how far apart cells are in a
element (or an element that is made to be table-like via display: table;).
It takes any of the lengths of CSS.
Notably, it only has any effect at all if the table is using the default border-collapse: separate; and has no effect at all when border-collapse: collapse; is set.
See the Pen
Table with Rounded Cells by Chris Coyier (@chriscoyier)