Why setting the z-index attribute is invalid_html/css_WEB-ITnose

Why setting the z-index attribute is invalid:

Specific conditions are required for the z-index attribute to take effect, otherwise of course it will not take effect. The following is a brief introduction to two situations in which it does not take effect.

1. The object does not have absolute positioning or relative positioning applied:

The object must have absolute positioning or relative positioning applied before the z-index attribute can take effect.

2. Browser compatibility results in:

For example, the select drop-down box cannot be covered by a div under the IE6 browser, although the div object uses absolute positioning and the z-index attribute value is set It's still not big enough.

For the solution, please refer to the chapter on the solution to the problem that div cannot cover the select drop-down box under IE6 browser.

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