Detailed explanation of CSS box model with pictures and text

When I first came into contact with the web, I was in college. The first web page I wrote was a login page. At that time, it used a table layout, which was quite satisfactory. After coming into contact with CSS, I always use p+css for layout, which achieves the separation of performance and structure and is very flexible. Although I have been exposed to the layout method of CSS for a long time, I don't use it often, so I have forgotten many things. Recently, I have been tinkering with the layout of CSS, so I wanted to record it here as my own study notes.

css box model is a core concept in css. In a web page, we can regard all web page elements as a box. A box consists of four parts: margin, border, inner margin, and content, as follows picture.

The functions of these four parts will be explained from outside to inside.

• margin (margin): represents the margin between this element and other elements. It should be noted that if two adjacent elements are If the margin value is set, the largest value shall prevail. For example, if there are two adjacent p's, the upper p sets margin: 30px, and the lower p sets margin: 50px, then the distance between the last two elements will not be 30+20=50px, but will be 30px.

• border (border): represents the border of this web page element. The border can set the size, background (color or picture), style (implementation or dotted line, etc.).

• padding (padding): represents the distance between the element content and the border. You can call it the white space of the element.

• content (content): represents the content area of ​​the element, such as the size of the text.

Among them, margins, borders, and padding can be applied to the top, bottom, left, and right sides of the element, or to each individual side. In particular, the margins can also be set to negative values. In some special occasions, negative values ​​for the margins are needed.

Generally, we set the width and height of an element, usually the width and height of the padding+content area, excluding margin and border.

When I set the background color of an element, the background will only be applied to the area within the border of the element, that is, padding+content, and the background color of the margin and border areas will not be changed.

An example will be demonstrated below. The code is as follows:

 
     
     
        
    

    
        

            
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The effect is as follows:

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