column-rule: dotted;
column-rule: solid 8px;
column-rule: solid blue;
column-rule: thick inset blue;

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

/* Same as "medium dotted currentcolor" */
p.foo {
  column-rule: dotted;
}

/* Same as "medium solid blue" */
p.bar {
  column-rule: solid blue;
}

/* Same as "8px solid currentcolor" */
p.baz {
  column-rule: solid 8px;
}

p.abc {
  column-rule: thick inset blue;
}

<p class="content-box">
  This is a bunch of text split into three columns. Take note of how the
  `column-rule` property is used to adjust the style, width, and color of the
  rule that appears between the columns.
</p>

.content-box {
  padding: 0.3em;
  background: #ff7;
  column-count: 3;
  column-rule: inset 2px #33f;
}