I'm not sure I follow. The spec page at
(19) if (column-width != auto) and (column-count != auto) then
(20) N := min(column-count, floor((available-width + column-gap) / (column-width + column-gap)))
(21) W := ((available-width + column-gap) / N) - column-gap;
I don't where the spec says how to determine the "available-width" value, unless I'm missing something. Specifically, I don't see a reference to "the longest sentence in the block." In my case, the available width would be almost 100% of the screen. How is Chrome computing such a narrow width?