Property Reference - CSS Reference - page 174

Name
column-rule
Values:
<'column-rule-width'> || <'border-style'> || [ <color>
Initial value:
See individual properties
Applies to:
Elements laid out using multiple columns
Inherited:
No
Computed value:
Same as declared value
Description:
A shorthand property that defines the width, style, and color of the “rules” (vertical lines)
drawn between columns in an element laid out with multiple columns. Any value omitted is
set to the default value of the corresponding property. Note that if no border style is defined,
it will default to none and no column rule will be drawn.
Examples:
#d01 {column-rule: 5px solid red;}
#d02 {column-rule: 2em dashed green;}