Per spec, a non-auto value of column-count creates a multicol container, see https://www.w3.org/TR/css-multicol-1/#the-multi-column-model https://www.w3.org/TR/css-multicol-1/#cc "An element whose column-width or column-count property is not auto establishes a multi-column container (or multicol container for short), and therefore acts as a container for multi-column layout." This is noticeable when the element has a fixed height: in this case the content should be fragmented into columns that overflow in the inline axis. See this testcase in e.g. WebKit vs Firefox: <div style="column-count: 1; height: 1.5em; border: solid;">1<br>2<br>3</div> https://software.hixie.ch/utilities/js/live-dom-viewer/?%3C!DOCTYPE%20html%3E%0A%3Cdiv%20style%3D%22column-count%3A%201%3B%20height%3A%201.5em%3B%20border%3A%20solid%3B%22%3E1%3Cbr%3E2%3Cbr%3E3%3C%2Fdiv%3E