CSS column-rule-style Property

The column-rule-style property sets the style of the rule between columns of an element.

column-rule-style: <border-style>

<border-style>Is a keyword defined by border-style describing the style of the rule. The styling must be interpreted as in the collapsing border model. Values are: none, hidden, dotted, dashed, solid, double, groove, ridge, inset and outset.

CSS

body {
   column-gap: 1em;
   column-rule-width: thin; 
   column-rule-style: solid;
   column-rule-color: black; 
}