What exactly is the merge of CSS vertical margins?

In-depth analysis of CSS vertical margin merging phenomenon

Vertical margin merging is a common problem in CSS style design. It refers to the vertical margins of adjacent block-level elements that do not simply superimpose, but merge occurs. Understanding its mechanisms and evasion methods is crucial to precisely controlling web layout.

What is vertical margin merge? Simply put, when two or more block-level elements are arranged vertically and there is no other content (such as inline elements or text) in the middle, their vertical margins are merged. The combined margins take a larger value; if the directions are opposite (one positive and one negative), then the difference between the absolute values ​​of the two is taken.

The specific situation is as follows:

1. Adjacent brother elements: Directly adjacent brother block-level elements (e.g. two<div> The vertical margins of the element) are merged.<li><p> <strong>Parent element and child element:</strong> If the block-level element is the only child element of the parent element and the parent element has no padding, the vertical margins of the parent element and the child element will be merged.</p></li> <li><p> <strong>Near block-level elements, the spacing is zero:</strong> even if there are blank lines or comments in the middle, the vertical margins of multiple adjacent block-level elements will be merged.</p></li> <p> How to avoid vertical margin merging:</p> <ol> <li><p> <strong>Use borders:</strong> Adding borders between adjacent block-level elements can effectively prevent merging.</p></li> <li><p> <strong>Use padding:</strong> Adding an inner margin to one or both of the elements can also avoid merging.</p></li> <li><p> <strong>Use block-level formatting context (BFC):</strong> Triggering BFC (such as setting <code>overflow: hidden; , float attribute, etc.) to create a new BFC to prevent margin merging. BFC is a page independent rendering area that can prevent margin merging and other layout features.

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