What is Flexbox?

It's a container used to layout items. We used to use float to layout.

Do I still need to use max-width?


How to use it to replace bootstrap?

  • For col-md-3, use percentage: flex-basis: 25%.
  • For pull or push, use order: n (by default is 0, 1 will move the item on main axis)
  • For visible-xs, use CSS display:none on different breakpoints. Note this has nothing to do with Flexbox

How to 'float' item on main axis?

  • order
  • margin: auto. > Prior to alignment via justify-content and align-self, any positive free space is distributed to auto margins in that dimension.

Good reference

How to center on both direction?

margin: auto is an alternative to justify-content: center and align-items: center

How to 'float' item on vertical axis?




  • display: flex
  • flex-direction
    • Notice that when you set the direction to a reversed row or column, start and end are also reversed. 1 2 3 -> (row-reversed) 3 2 1 So you can use this to reverse item orders on main axis.
  • flex-wrap (by default, all fit to one line)
    • there is an option wrap-reverse: flex items will wrap onto multiple lines from bottom to top. Which will basically move items on cross axis. See flexbox foggy level 24.
  • flex-flow = flex-direction | flex-wrap
    • so you can just use this one to reorder items on both main and cross axis
  • 2 axis:
    • main: justify-content
      • Note when center and wrap, only the wrapped items in next line will be centered.
      • when space-between: evenly space, with the first item aligned to one edge of the container and the last item aligned to the opposite edge.
    • cross:
      • align-items
        • it determines how the items as a whole are aligned within the container
        • interesting options: baseline, stretch (use to achive same height items)
      • align-content (when there is more space/multiple lines on cross axis)
        • it determines the spacing between lines


  • order (default: 0)
    • use to 'move' on main axis. For example, you can use order: -1 to achive bootstrap col-md-pull-3
  • align-self: this override the defalut align-items in container.
    • use to 'move' on cross axis
    • NOTE to vertical align this item, you don't need to add flex and align-items to the item, you could just use align-self on the item.
  • flex-grow (default: 0)
    • the number means how many propotion of AVAILABLE container space it can get. So one with 1 and one with 2 will get 1/3 and 2/3 space to grow.
  • flex-shrink (default: 1)
    • 0 means no shrink. Default 1 means everyone shrinks the same.
  • flex-basis (default: auto)
    • 'auto' keyword means "look at my width or height property" (which was temporarily done by the main-size keyword until deprecated).
  • flex = grow | shrink | basis (default: 0 1 auto)

Example on flex:

.item1{ flex: 2 0 50px} 
.item2{flex: 0 0 150px}
.item3{flex: 1 0 50px}` 

// if they take the whole container 600px, it'll ends up with this:
// item 1: (600 - 50 - 150 - 50) / (2+1) * 2 + 50 = 250px
// | item 1 250px | item 2 150px | item 3 15opx |

NOTE: float, clear and vertical-align have no effect on a flex item.

Other resources

Froggy level 24:

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