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Difference between auto, 0 and no z-index

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Aug 31, 2023 pm 11:41 PM

auto、0 和无 z-index 之间的区别

The position of elements in a web page is an important attribute assigned by developers. If your elements are not placed correctly, then it may appear nonsensical or unorganized. Therefore, it is very important for developers to allocate the position of each HTML element wisely.

Sometimes elements may overlap despite being assigned their respective positions. These overlapping elements can be stacked on top of each other and hide other elements. To solve this problem, CSS provides the z-index property for web design. In this article, we will learn about the z-index property of CSS. We will also discuss the different values of z-index and the differences between them.

What is the z-index attribute?

The z-index property of CSS enables developers to specify the order of elements that overlap on the z-axis (i.e. on-screen or off-screen). However, the z-index attribute only works on elements that have a position value other than static specified.

The stack level of an HTML element is determined by the z-index attribute. The position of an element on the Z-axis is called the "stack level" (as opposed to the X-axis or Y-axis). If the value is higher, the element will be placed closer to the top of the stacking order. This stacking arrangement is perpendicular to the viewport or monitor.

The natural stacking order of components on the Z-axis in an HTML page is affected by a variety of factors. These are elements with negative stacking context, non-positioned, non-floated, block-level elements, non-positioned, floated elements, inline elements, and positioned elements, all in display order.

grammar

element{
   z-index: values;
}

The following is the value of this attribute -

Auto - Overlapping order is the same as the parent's value. It's the default value.
Number - Overlapping sequences are specified as numbers, such as 1, 2, 3, etc.
Initial - Order set to default.
Inheritance - Overlapping order is inherited by the parent element.

Example

<!DOCTYPE html>
<html>
<head>
   <title>z-index property</title>
   <style>
      .demo1{
         font-family: cursive, Cochin, Georgia;
         background-color: red;
         position: absolute;
         top: 100px;
      }
      .demo2{
         font-family: cursive, Cochin, Georgia;
         background-color: #FFFF00;
         position: absolute;
         top: 100px;
         left: 300px;
         z-index: 2;
         width: 200px;
      }
   </style>
</head>
<body>
   <center>
      <h2 id="z-index-property"> z-index property </h2>
      <div class= "demo1"> This is an example. </div>
      <div class= "demo2"> This is an example. </div>
   </center>
</body>
</html>

Automatic value of z-index attribute

The auto value of the z-index attribute is the same element order as the parent element.

Example

<!DOCTYPE html>
<html>
<head>
   <title>Auto value of z-index property</title>
   <style>
      .demo1{
         font-family: verdana,'cursive';
         background-color: #FFFF00;
         position: absolute;
         top: 120px;
         z-index: auto;
      }
      .demo2{
         font-family: cursive, Cochin, Georgia;
         background-color: red;
         position: absolute;
         top: 200px;
         z-index: auto;
      }
   </style>
</head>
<body>
   <center>
      <h2 id="z-index-property">z-index property</h2>
      <p class= "demo1"> This is an example. </p>
      <p class= "demo2"> This is an example. </p>
   </center>
</body>
</html>

Zero value for z-index attribute

The zero value of the z-index attribute is the numerical value of the element order. Specify a z-index value of 0 to create stacked content. For example, if we have two elements element1 and element2, their z-indexes are 1 and 0 respectively. Therefore, element 1 will be stacked on top of element 2. And if their z-indexes were -1 and 0 respectively, element 1 would be stacked underneath element 2. Consider the following example.

Example

<!DOCTYPE html>
<html>
<head>
   <title>Zero value of z-index property</title>
   <style>
      .demo1{
         font-family: cursive, Cochin, Georgia;
         background-color: #FF0000;
         position: absolute;
         top: 120px;
         z-index: 0;
      }
      .demo2{
         font-family: cursive, Cochin, Georgia;
         background-color: red;
         position: absolute;
         top: 100px;
         left: 300px;
         z-index: 0;
         width: 200px;
      }
   </style>
</head>
<body>
   <h1 id="Tutorialspoint">Tutorialspoint</h1>
   <h2 id="z-index-property">z-index property</h2>
   <p class= "demo1">This is an example.</p>
   <p class= "demo2">This is an example.</p>
</body>
</html>

z-index attribute has no value

The value of the z-index attribute will usually not be the same as the auto value.

Example

<!DOCTYPE html>
<html>
<head>
   <title>No value for z-index property</title>
   <style>
      .demo{
         font-family: cursive, Cochin, Georgia;
         background-color: #FFFF00;
         position: absolute;
         top: 120px;
      }
   </style>
</head>
<body>
   <h2 id="z-index-property">z-index property</h2>
   <p class= "demo">This is an example.</p>
</body>
</html>

in conclusion

A challenging topic is stacking contexts in CSS. In this article, we comprehensively describe how stacking context on a web page is affected by z-index, which, when fully understood, translates into powerful CSS properties. Now that they are familiar with this feature, new developers should be able to use it effectively and avoid some common problems that can occur. Advanced developers should also become more aware of how the proper application of z-index can solve various layout challenges and provide a variety of creative CSS design options.

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