What does z-index mean?

z-index is a CSS property that controls the order in which elements overlap on the page, similar to the order in which paper is stacked. Here's how it works: Every element has a default z-index value of 0. Elements with higher z-index values ​​will overwrite elements with lower z-index values. z-index can be used to create floating elements, control the order of overlapping elements, and create three-dimensional effects. When using, you need to consider things such as avoiding overuse, using negative values, and paying attention to browser compatibility.

What is z-index?

z-index is a property in CSS (Cascading Style Sheets) used to control the order in which elements overlap on the page. It specifies the position of an element relative to other elements on the page, similar to the order in which paper is stacked.

How z-index works

Every HTML element has a default z-index value of 0. Elements with higher z-index values ​​will overwrite elements with lower z-index values. For example:

#element1 {
  z-index: 10;
}

#element2 {
  z-index: 20;
}

In this case, #element2 will overwrite #element1 because it has a higher z-index value.

Uses of z-index

z-index is widely used in web design:

• Create floating elements: Such as floating menus or tool tips, they can float above the page content.
• Control the order of overlapping elements: For example, in a drop-down menu, the z-index value of the menu item is higher than the z-index value of the menu trigger.
• Create three-dimensional effects: By setting different z-index values, you can create elements with the illusion of depth.

Notes on z-index

When using z-index, you need to consider the following:

• Avoid overuse: High z-index values ​​may cause page loading delays and performance issues.
• Use negative values: Use negative values ​​to place elements at the bottom of the stacking order.
• Browser compatibility: Different browsers may have different support for z-index, so this needs to be considered when designing across browsers.

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