column-rule-style

/* <'border-style'> values */
column-rule-style: none;
column-rule-style: hidden;
column-rule-style: dotted;
column-rule-style: dashed;
column-rule-style: solid;
column-rule-style: double;
column-rule-style: groove;
column-rule-style: ridge;
column-rule-style: inset;
column-rule-style: outset;

/* Global values */
column-rule-style: inherit;
column-rule-style: initial;
column-rule-style: revert;
column-rule-style: unset;

<p>This is a bunch of text split into three columns.
   The `column-rule-style` property is used to change
   the style of the line that is drawn between columns.
   Don't you think that's wonderful?</p>

p {
  column-count: 3;
  column-rule-style: dashed;
}