What is the maximum and minimum value for z-index?

Question

I was arguing with some friends about putting 99999 in the z-index to ensure that the element has the highest priority of overlapping over another element.

But when I thought about it, I got a little curious:

• What is the maximum value for z-index?
• What is the minimum value for z-index, as it supports negative values?

Answer 1

Information taken from the Internet:

│ Browser              │ Max z─index value │ When exceeded, value changes to: │
╞══════════════════════╪═══════════════════╪══════════════════════════════════╡
│ Firefox 0 - 2        │ 2147483647        │ element disappears               │
├──────────────────────┼───────────────────┼──────────────────────────────────┤
│ Firefox 3            │ 2147483647        │ 0                                │
├──────────────────────┼───────────────────┼──────────────────────────────────┤
│ Firefox 4+           │ 2147483647        │ 2147483647                       │
├──────────────────────┼───────────────────┼──────────────────────────────────┤
│ Safari 0 - 3         │ 16777271          │ 16777271                         │
├──────────────────────┼───────────────────┼──────────────────────────────────┤
│ Safari 4+            │ 2147483647        │ 2147483647                       │
├──────────────────────┼───────────────────┼──────────────────────────────────┤
│ Internet Explorer 6+ │ 2147483647        │ 2147483647                       │
├──────────────────────┼───────────────────┼──────────────────────────────────┤
│ Chrome 29+           │ 2147483647        │ 2147483647                       │
├──────────────────────┼───────────────────┼──────────────────────────────────┤
│ Opera 9+             │ 2147483647        │ 2147483647                       │

Read more here.

Answer 2

If you browse the latest version of the specification and for na property list and arrive at the z-index property, there has the last definition of the same: 

• Name: z-index
• Value: auto | < integer >
• Initial: auto
• Applies to: positioned Elements
• Inherited: in the
• Percentages: N/A
• Computed value: the keyword auto or an integer
• Canonical order: per Grammar
• Animatable: < integer >
• Animation type: by computed value

The value is the type integer, which is to say 2³² (-2147483648 to [phone]).

Now if browsers will follow this value to the letter, it would be another task to be discovered.

In this other answer at stackouverflow in English, has more elaborate answers.