zindex:是rn在0.30開始支援的屬性。
zIndex controls which components display on top of others. Normally, you don’t use zIndex. Components render according to their order in the document tree, so later components draw over earlier ones. zIndex may be useful if you have animations or custom modal interfaces where you don’t want this behavior。
zindex屬性可以控制組件顯示在其他元件上，正常情況，你不需要使用。元件通過元件樹，後一個覆蓋前一個。zindex可以用於動畫或者自定義modal,讓你決定誰可以顯示在上面。