css positioning z-index problem

1. There is a bug in element level masking in some browsers;
   
   The z-index of a certain element is set too large, causing it to never be covered;
   
   js dynamically calculates z-index, causing the element coverage relationship to be uncontrollable

   

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   It can be understood like this: the positioning tree contains all elements in the dom tree whose position is not staitc. The hierarchical relationship between non-sibling elements can be compared as follows:
   
   1. Traverse the parent node of the positioning tree upward until two elements are sibling elements.
   
   2. Let’s make the final comparison based on the above conclusion. Higher-level elements will move closer to the user's display and cover lower-level elements.
   
   
   Example 1: Assume that the positions of all elements marked in red in the above picture are not static; and z-index=1. According to the above comparison rules, we can know:
   
   1. c > (b && b *) > (a && a *) That is, the level of all positioned elements of elements c and c is higher than a and b
   
   2. m > h, g > k, d > m
   
   Example 2: Assume that the position of a is not static, the z-index attribute does not exist. The z-index of the sub-elements of a in the positioning tree are 1, 2, 3, 4... Other positioning elements z-index: 1:
   
   1. According to the following three conclusions: Under IE6/7, b > (a && a *) means that the level of element b is higher than a and all positioned elements of a. Under other browsers: i > h > b > d. Please indicate the source for reprinting: css positioning z-index problem