the first two parameters are pretty much self-explanatory: flex-grow set to 1 means the item can grow if necessary, flex-shrink set to 0 means it can’t decrease in size. The interesting one is the last parameter flex-basis. I’ve checked CSS tricks and found "It specifies the initial size of the flex item, before any available space is distributed according to the flex factors. " Not sure I understand how it kicks in and why did you use percentage instead of just 0 zero?