This property can help you create responsive designs that fit different screen sizes. Especially in the presence of the column-count property (which has precedence), you must specify all related length values to achieve an exact column width. In horizontal text these are width, column-width, column-gap, and column-rule-width.

/* Keyword value */
column-width: auto;

/* <length> values */
column-width: 60px;
column-width: 15.5em;
column-width: 3.3vw;

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

The column-width property is specified as one of the values listed below.

<length>

Indicates the optimal column width. The actual column width may differ from the specified value: it may be wider when necessary to fill available space, and narrower when the available space is too small. The value must be strictly positive or the declaration is invalid. Percentage values are also invalid.

auto

The width of the column is determined by other CSS properties, such as column-count.

column-width = 
  auto                                |
  <length [0,∞]>                      |
  min-content                         |
  max-content                         |
  fit-content( <length-percentage> )  

<length-percentage> = 
  <length>      |
  <percentage>  

HTML

<p class="content-box">
  Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy
  nibh euismod tincidunt ut laoreet dolore magna aliquam erat volutpat. Ut wisi
  enim ad minim veniam, quis nostrud exercitation ullamcorper suscipit lobortis
  nisl ut aliquip ex ea commodo consequat.
</p>

CSS

.content-box {
  column-width: 100px;
}

Result

• Multiple-column Layout (Learn Layout)
• Basic Concepts of Multicol