这个规范描述了 margin 和 padding 属性，它们在 CSS 框内和周围创建间距。以后可能会扩展到包括边框（目前在 [css-backgrounds-3] 中描述）。
Each box has a content area (which contains its content—text, descendant boxes, an image or other replaced element content, etc.) and optional surrounding padding, border, and margin areas; the size of each area is specified by corresponding properties, and can be zero (or in the case of margins, negative). The following diagram shows how these areas relate and the terminology used to refer to the various parts of the box:
标签：Box,padding,Level,content,Model,CSS From： https://www.cnblogs.com/facenano/p/16872894.html