column-rule

column-rule: dotted;

column-rule: solid 6px;

column-rule: solid blue;

column-rule: thick inset blue;

<section id="default-example">
  <p id="example-element">
    London. Michaelmas term lately over, and the Lord Chancellor sitting in
    Lincoln's Inn Hall. Implacable November weather. As much mud in the streets
    as if the waters had but newly retired from the face of the earth, and it
    would not be wonderful to meet a Megalosaurus, forty feet long or so,
    waddling like an elephantine lizard up Holborn Hill.
  </p>
</section>

#example-element {
  columns: 3;
  column-rule: solid;
  text-align: left;
}

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

/* Глобальные значения */
column-rule: inherit;
column-rule: initial;
column-rule: unset;

/* Аналогично "medium dotted currentColor" */
p.foo {
  column-rule: dotted;
}

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

/* Аналогично "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;
}