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Detailed explanation of the usage of z-index attribute in CSS in cascading layout
In web development, it is often necessary to cascading layout of elements to achieve cascading layout between elements. coverage effect. The z-index property in CSS is used to control the stacking order of elements. This article will introduce the use of z-index attributes in cascading layout in detail and provide specific code examples.
1. The basic concept of z-index attribute
The z-index attribute is used to specify the stacking order of elements in a cascading layout. The value is an integer. The larger the value, the closer the element is to the front, that is, it is displayed on the upper level. If the z-index values of two elements are the same or the z-index attribute is not set, the stacking order is determined based on their order in the HTML code. The z-index attribute can only be applied to elements whose position attribute value is relative, absolute, or fixed, and is invalid for elements with other position attribute values (such as static).
2. Usage of z-index attribute
<!DOCTYPE html> <html> <head> <style> .box1 { position: relative; z-index: 1; } .box2 { position: relative; z-index: 2; } .box3 { position: relative; z-index: 3; } </style> </head> <body> <div class="box1">Box 1</div> <div class="box2">Box 2</div> <div class="box3">Box 3</div> </body> </html>
In the above code, box1, box2 and box3 respectively represent three elements with different z-index values. Box3 has the largest z-index value, so it will be on the top layer in the stacked layout, box2 is in the middle, and box1 is on the bottom layer.
<!DOCTYPE html> <html> <head> <style> .parent { position: relative; z-index: 1; } .child1 { position: relative; z-index: 2; } .child2 { position: relative; z-index: 3; } </style> </head> <body> <div class="parent"> <div class="child1">Child 1</div> <div class="child2">Child 2</div> </div> </body> </html>
In the above code, parent represents the parent element, and child1 and child2 represent two child elements. Although the parent element sets the z-index value, it has no effect on the stacking order of the child elements. child2 still has the largest z-index value, so it will be on top in the stacked layout.
3. Notes on the z-index attribute
4. Summary
The z-index attribute plays an important role in the cascading layout in CSS. You can control the cascading order of elements by setting the z-index value. Through the sample code provided in this article, readers can better understand and apply the z-index attribute to achieve coverage effects between various elements.
It should be noted that the z-index attribute is only valid for positioned elements and takes effect within the parent element. In actual development, setting the z-index value reasonably according to actual needs can achieve a more elegant and hierarchical page layout effect.
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