If some of them still use ie6 and you have to enable them to use your website, you have to propose another way to display. I just learned about flexbox yesterday so now Im all anxious to learn more. Then using media queries to make appropriate adjustments based on the users screen. Ref: http://msdn.microsoft.com/en-us/library/ie/dn265027(v=vs.85).aspx I think for align-content, the container should already has been propped up by some elements or in a fixed height. How to set 3 items per row using flex when item has margin and border You can use width: calc (100%/3 - 12px); on .item. wrong main size when flex-driection is column. Oh, and the purple box now fills the entire width of the screen, which looks good, but is it the first 1 doing that since it is clearly taking up more than 20% of the container now? I suspect that relatively few people want to settle for what we have now and just work with that. The value must be a number, default value is 0. For example, if I have a 500 pixel-wide container, flex-direction is row, and I have three flex items each 100 pixels wide, then I have 200 pixels of positive free space, which could be distributed between the items if I wanted them to fill the container. Good stuff. Resize the width below 900px and youll see what happens. CSS3 flexbox layout max 3 child items on one line, Centering content horizontally using flexbox, Align two elements on the same line using flex: one left and one right, Make background color extend into overflow area, Using object-fit on a