尺寸優先順序
舉例：若有設 flex-basis 跟 width，優先考慮 flex-basis
| 優先權 (由大到小) | 屬性 |
|---|---|
| 5 | Max-width |
| 4 | Min-width |
| 3 | Flex-basis |
| 2 | Width |
| 1 | Content-width |
flex 屬性縮寫
flex: grow shrink basis
flex: 1 1 0 /* is the same as flex: 1 */
flex: 2 2 0 /* is the same as flex: 2 */
flex: 3 /* is the same as flex: 3 3 0 */