Flex containers are not block containers, and so some properties that were designed with the assumption of block layout don’t apply in the context of flex layout. In particular:
the column-* properties in the Multi-column Layout module [CSS3COL] have no effect on a flex container.
float and clear do not create floating or clearance of flex item, and do not take it out-of-flow.
vertical-align has no effect on a flex item.
the ::first-line and ::first-letter pseudo-elements do not apply to flex containers, and flex containers do not contribute a first formatted line or first letter to their ancestors.
If an element’s specified display is inline-flex, then its display property computes to flex in certain circumstances: the table in CSS 2.1 Section 9.7 is amended to contain an additional row, with inline-flex in the "Specified Value" column and flex in the "Computed Value" column.
用於塊狀元素的屬性對flex 容器不起作用
Flex 容器不是塊級容器，因此一些專用於塊狀布局的屬性，對Flex 布局不起作用。比如：
2. float 和 clear 不能讓彈性容器下的項目擺脫文檔流，或清除浮動。
3. vertical-align 垂直居中不起作用。（flex布局下，垂直居中更簡單舒適：看我這里的一篇文章）
4. 偽類元素 ::first-line 和 ::first-letter
flex This value causes an element to generate a block-level flex container box.
inline-flex This value causes an element to generate an inline-level flex container box.
flex，inline-flex，inline-block 區別
flex： 將對象作為塊級彈性伸縮盒顯示。
inline-flex：將對象作為內聯彈性伸縮盒顯示。
inline-block: 將對象呈現為inline對象，但是對象的內容作為block對象呈現。
比如說，inline元素的margin和padding屬性，水平方向的padding-left, padding-right, margin-left, margin-right都產生邊距效果；但豎直方向的padding-top, padding-bottom, margin-top, margin-bottom不會產生邊距效果。
那么，對於inline-block來說，margin和padding的垂直方向的邊距，則會產生邊距效果。
Note: Some values of display normally trigger the creation of anonymous boxes around the original box. If such a box is a flex item, it is blockified first, and so anonymous box creation will not happen. For example, two contiguous flex items with display: table-cell will become two separate display: blockflex items, instead of being wrapped into a single anonymous table.
display的一些值，很可能在該容器觸發創建匿名框機制。（匿名框有塊級的，和內聯的。）
如果是一個彈性容器的伸縮項目，它首先被塊級化，因此不會創建匿名框。比如，兩個相鄰的伸縮項目，display值為 table-cell時，是兩個獨立的塊級項目，而不會包裹成一個單獨的匿名表格。