column-fill

The column-fill CSS property controls how contents are partitioned into columns. Contents are either balanced, which means that contents in all columns will have the same height or, when using auto, just take up the room the content needs. 

Formal syntax: 
auto | balance | balance-all

column-fill: auto;
column-fill: balance;

/* Global values */
column-fill: inherit;
column-fill: initial;
column-fill: unset;

auto

Is a keyword indicating that columns are filled sequentially.

balance

Is a keyword indicating that content is equally divided between columns.

.content-box {
  column-count: 4;
  column-rule: 1px solid black;
  column-fill: balance;
  height: 200px;
}