Document horizontal/vertical alignment properties

Right now vertical/horizontal alignment properties are mentioned in the supported CSS properties section, but this is not ideal - we need to document and show examples of using them.

The right place for them would likely be in the various LayoutContainer examples maybe, unless there's a better place (I can't think of one right at the moment).

從支援的 CSS 屬性區段開始，並檢視現有的 LayoutContainer 範例。在版面配置文件中最適當的位置，透過使用範例記錄水平方向和垂直方向的對齊屬性；當兩個屬性都獲得清楚的說明和示範時，工作即完成。