flex-shrink dictates how negative free space should be distributed. When there is no free space, it is irrelevant. In addition to that, below a certain width,

flex-shrink dictates how negative free space should be distributed. When there is no free space, it is irrelevant. In addition to that, below a certain width, the CSS on the parent UL is being changed from flex-wrap: nowrap; to flex-wrap: wrap;, so when the container shrinks to a width smaller than the sum of the flex-basis of all elements, it will wrap. Keep in mind I haven't read the flex spec yet, though, so that's based on observation not spec.