We all use margin in CSS, but setting margin to a negative number may not be easy to handle. Negative margin values are not a hack, and negative margin values follow the document flow; if negative margin values are used to move an element upward, then it is relevant Elements will also be displaced accordingly; negative margin values are well compatible with various browsers.
1. There are two borders with different background colors. No matter which side increases, the other side also becomes higher
2. Implement adaptive
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