Why does front-end fixed positioning have movement problems?

Why does the front-end fixed positioning move?

When doing front-end development, we often use the position attribute in CSS to control the positioning of elements. Among them, fixed positioning (position: fixed) is a commonly used positioning method, which allows elements to be positioned relative to the browser window and remain in a fixed position on the page.

However, sometimes we encounter a problem: when using fixed positioning, the element will move, that is, the position of the element is no longer fixed, but changes as the page scrolls.

So, why does this movement phenomenon occur?

First of all, it needs to be clear that fixed positioning is positioned relative to the browser window, not to a specific element of the page. This means that when the page is scrolled, fixedly positioned elements will move with the window.

Secondly, common causes of fixed positioning movement are the collapse of the parent container caused by margin collapse in the CSS box model and floating elements.

First let’s take a look at the margin folding situation. Margin folding means that when the vertical margins of two adjacent boxes meet, their margins will merge. Specifically, there are the following situations:

1. When adjacent boxes have positive values ​​at the same time margin, their margins will be merged into one larger margin, causing fixed-positioned elements to be offset.
2. When one adjacent box has a positive margin and the other has a negative margin, their margins will offset each other, which may result in inaccurate positioning of fixedly positioned elements.

So, when we use fixed positioning, we need to pay attention to whether the adjacent elements of the element have margin folding to avoid unexpected movement.

In addition, floating elements can easily cause fixed positioning elements to move.

Floated elements are separated from the normal document flow and positioned relative to their containing block. When there is a floating element in the containing block of a fixedly positioned element, the fixedly positioned element will be positioned relative to the floating element, causing movement.

In order to solve this problem, we need to add a clear float style to the containing block. You can use the clear attribute, or use overflow:hidden to clear the float.

In addition to the above reasons, there are other situations that may cause fixedly positioned elements to move, such as using the transform attribute, using CSS animation effects, etc.

When using fixed positioning, you can use developer tools to check the style attributes of the element, find out whether there are other styles or elements that affect the position of the fixed positioning, and make timely adjustments.

In summary, the main reasons why fixedly positioned elements move include margin collapse and the collapse of the parent container caused by floating elements. To avoid movement, we need to pay attention to whether the margins of adjacent elements of the element are collapsed, and whether there are positioning errors caused by floating elements. At the same time, use CSS properties and styles rationally to avoid other factors that affect fixed positioning.

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