What is z-order?
John Zukowski To understand z-order, think first of x and y positioning. The x-y coordinate space places position (0, 0) at the top-left corner of the screen. Increasing the x value moves the position to the right. Increasing the y value moves the position down. Where does that leave position z? Z-order controls how components are drawn on top of one another. The 0 layer is the highest layer, or the one drawn last. Layer 1 is next, then 2, and so on.