Why the overflow attribute does not work when float clearing is invalid, reason analysis

Why the overflow attribute is invalid for float clearing, reason analysis, specific code examples are needed

Float (float) is one of the commonly used layout methods in CSS, and its function is to let An element is taken out of the document flow, allowing it to float to the left or right of its parent element. However, floating elements can cause some layout problems. One of them is that the floating elements cannot support the height of the parent element, causing the height of the parent element to collapse. To solve this problem, we usually use the technique of clearing floats.

When clearing floats, the commonly used attribute is overflow:hidden. Its function is to create a new BFC (block-level formatting context) to contain floating elements. However, sometimes we find that setting overflow:hidden does not have the effect of clearing floats. Why is this? Let us analyze it together.

First, we need to understand how the overflow attribute works. When overflow:hidden is set, the element will create a new BFC. One of the characteristics of the BFC is that it will contain floating elements. Therefore, under normal circumstances, setting overflow:hidden can indeed clear the floating, allowing the parent element to display the floating child elements normally and expand the height.

However, in some special cases, overflow:hidden will fail and will not work. One of the common situations is that the height of the parent element is stretched by the floating child elements, but the parent element itself does not set any height. At this time, setting overflow:hidden does not clear the float.

This is because when an element does not set a specific height, its height is expanded by the content by default. The floated element no longer occupies a position in the document flow, so the parent element cannot sense the height of the floated child element and thus cannot support itself in relation to the child element.

In order to solve this problem, we can use other methods to clear floats. One common method is to add an empty block-level element and clear its float. The specific code is as follows:

<style>
    .clearfix:after {
        content: "";
        display: block;
        clear: both;
    }
    .box {
        width: 200px;
        border: 1px solid #ccc;
    }
    .float-left {
        float: left;
        width: 100px;
        height: 100px;
        background-color: red;
        margin-right: 20px;
    }
</style>

<div class="box clearfix">
    <div class="float-left"></div>
    <div class="float-left"></div>
    <!-- 添加一个空的块级元素用于清除浮动 -->
    <div class="clearfix"></div>
</div>

In the above code, we added a clearfix class to the parent element box, and added an empty block-level element to it using the :before or :after pseudo-element, and added It performs a clear float operation. This way, the float is cleared and the height of the parent element is stretched correctly.

In addition to the above methods, there are other ways to clear floats, such as using clearfix class to clear floats, or using a specialized float clearing class library. In different situations, you may need to choose different float clearing methods. In actual development, it is important to choose the most suitable float clearing method according to specific scenarios.

In summary, setting overflow:hidden may not be effective in clearing the height collapse problem caused by floating. In some special cases, the height of the parent element is stretched by the floating child elements, and setting overflow:hidden has no effect. At this point, we can use other methods to clear the float correctly and make the parent element expand its height correctly.

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