(First of all, yes, I've read all the documentation and flex-box reference multiple times.) I have two empty, plain VisualElement objects. Their parent is a simple container VisualElement with display:flex and flex-direction:column. In other words, I just want to stack two VisualElements on top of each other and have them fill all available space. I've set the flex-grow of the child VisualElements each to 1 and the flex-shrink of each to 0. These elements are contained within a custom EditorWindow which contains no other elements, i.e. it's: rootVisualContainer parentFlexContainer (VisualElement, flex-direction:column) flexItem1 (VisualElement, flex-grow:1, flex-shrink:0, width/height:auto) flexItem2 (VisualElement, flex-grow:1, flex-shrink:0, width/height:auto) The width and height of flexItem1 and 2 are 'auto'. Everything I understand about flex layout tells me that, given this hierarchy, flexItem1 and flexItem2 should fill the EditorWindow in such a way that they each take up half the vertical space of the window, i.e. the bounds should look like: But they don't. Instead, they don't take up any space whatsoever, despite their flex-grow properties and width/height set to auto. Is this a bug, or am I fundamentally misunderstanding flex layout?