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Analysis of the reasons why fixed positioning cannot be used in HTML

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Jan 20, 2024 am 10:20 AM

Analysis of the reasons why fixed positioning cannot be used in HTML

In HTML, fixed positioning (fixed positioning) refers to the positioning of elements relative to the position of the browser window. Does not change position as the page scrolls. However, in some cases we find that we cannot achieve the effect we want using fixed positioning. This article will analyze the reasons why fixed positioning cannot be used in HTML and give specific code examples.

1. Reasons why fixed positioning cannot be used

The parent element is not set to relative positioning or absolute positioning

When an element wants to use fixed positioning, Its parent element must at least be set to relative positioning (position: relative;) or absolute positioning (position: absolute;). If the parent element does not set the positioning attribute, the child element cannot use fixed positioning.

The overflow attribute setting of the parent element

If the overflow attribute of the parent element is set to hidden (overflow: hidden;), the child element will be hidden when using fixed positioning . Therefore, make sure the overflow attribute of the parent element is not hidden, or position the child element outside the parent element.

Restrictions on element positioning relative to the browser viewport

Fixed positioning is positioned relative to the browser window viewport, therefore, there are the following restrictions:## The

element cannot be affected by other elements, even if other elements are positioned. It also does not affect fixedly positioned elements.

If the positioning attribute (position) of the element is overridden by other styles, the fixed positioning will not take effect. Make sure the element's positioning properties are not overridden or set incorrectly.

2. Code Example

The following is a specific code example that demonstrates why fixed positioning cannot be used in HTML.

<!DOCTYPE html>
<html>
<head>
<style>
.container {
  width: 100%;
  height: 2000px;
}

.fixed {
  position: fixed;
  top: 20px;
  left: 20px;
  background-color: red;
  color: white;
  padding: 10px;
}

.overflow-hidden {
  overflow: hidden;
}

.relative-parent {
  position: relative;
}

.absolute-parent {
  position: absolute;
  top: 0;
  left: 0;
}

.other-element {
  position: relative;
  top: 50px;
  left: 50px;
  background-color: blue;
  color: white;
  padding: 10px;
}
</style>
</head>
<body>
<div class="container overflow-hidden">
  <div class="fixed">我应该是固定定位，但我被隐藏了</div>
</div>

<div class="container relative-parent">
  <div class="fixed">我是固定定位，因为父元素设置了相对定位</div>
</div>

<div class="container absolute-parent">
  <div class="fixed">我是固定定位，因为父元素设置了绝对定位</div>
</div>

<div class="container">
  <div class="other-element">我不影响固定定位的元素</div>
  <div class="fixed">我是固定定位，因为没有其他元素影响我</div>
</div>
</body>
</html>

The above code first demonstrates the situation where the fixed positioning of the child element is hidden when the overflow attribute of the parent element is set to hidden. Then, the application of fixed positioning is demonstrated by setting the relative positioning and absolute positioning of the parent element. Finally, by adding other elements, it was verified that the fixed positioning is not affected by other elements.

Summary

This article analyzes the reasons why fixed positioning cannot be used in HTML, and gives specific code examples to demonstrate these reasons. When writing HTML and CSS, special attention needs to be paid to addressing the above issues to ensure that elements use fixed positioning correctly.

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