Turns out there are specific CSS properties for columns:
Here’s what worked for my case:
.featured {
-moz-column-count: 3;
-moz-column-width:245px;
-moz-column-gap: 40px;
-webkit-column-count: 3;
-webkit-column-gap : 40px;
-webkit-column-width:245px;
-moz-column-rule-color: #ccc;
-moz-column-rule-style: solid;
-moz-column-rule-width: 1px;
-webkit-column-rule-color: #ccc;
-webkit-column-rule-style: solid ;
-webkit-column-rule-width: 1px;
}
And two refs for several other ways to go about it.