The column-width CSS property suggests an optimal column width. This is not a absolute value but a mere hint. Browser will adjust the width of the column around that suggested value, allowing to achieve scalable designs that fit different screen size. Especially in presence of the column-count CSS property which has precedence, to set an exact column width, all length values must be specified. In horizontal text these are width, column-width, column-gap, and column-rule-width.

[Webplatform](docs.webplatform.org/wiki/css/properties/column-width "Webplatform")
[Mozilla docs](https://developer.mozilla.org/en-US/docs/Web/CSS/column-width "Mozilla")
[Caniuse](http://caniuse.com/#feat=multicolumn "Caniuse")