If the father level set the property of flex, the children level box will has the default property like flex: 0 1 0, corresponding to the following property flex-shrink: 0, flex-grow: 1, flex-basis: 0. In that case, your width property is invalid.
If you want to set the fix width, setting children property to flex: 0 0 YOUR_WIDTH(the flex of the father level’s property must set to flex-direction: row;), but the property of width is also invalid.
Or setting children property to flex: 0 0 auto. Then the property of width is work.
