1. container & item
   • display: flex —> 宣告元件成 flex container
2. flex-direction
   • row
   • row-reverse
   • column
   • column-reverse
3. flex-wrap
   • no-wrap
   • wrap
   • wrap-reverse
4. flex-flow
   • flex-flow: <flex-direction> <flex-wrap>
5. justify-content ( 主軸 )
   • flex-start
   • flex-end
   • center
   • space-between
   • space-around
   • space-evenly
6. align-item ( 次軸 )
   • flex-start
   • flex-end
   • center
   • baseline
   • stretch
7. flex-basic
8. flex-grow
9. order