column-rule

Column rules are essentially borders between each column. The
snippet
column-rule
property specifies the color, style, and width of the column rules. The rule will appear in the middle of the column gap.

This property is actually shorthand for the column-rule-color, column-rule-style, and column-rule-width properties.

The syntax for the value is exactly the same as for border and the related border-width, border-style, and border-color properties. The width can be any length unit, just like border-width, including the key terms of medium, thick, and thin. And the color can be any supported color value.

snippet
-webkit-column-rule: 1px solid #CCCCCC;
-moz-column-rule: 1px solid #CCCCCC;
column-rule: 1px solid #CCCCCC;
Related Tutorial
5. columns