What is a box model?

What is the box model?

Any tag in the web page is equivalent to a box model, and all box models have five necessary attributes: width, height, padding, border, margin.

So in How to calculate the actual width of a box model in a web page? ? ? ?

　For example:

　　　

The width of the above div should be: width+2*padding+2border=300+2*20+2*1=342px;

padding: Padding: the distance between content and border.

The four attributes of padding: padding-top, padding-bottom, padding-left, padding-right.

width: width.

height: height.

border: border.

Common border writing method: border:1px solid #ccc; respectively represents the width, line type and color of the border.

Common line types are: solid (solid line), dashed (dashed line), dotted (dotted line).

The three basic attributes of the border: border-width (width of the border), border-style (line type of the border), border-color (color of the border);

maigin: outer edge Distance.

The four basic attributes of margin: margin-top, margin-bottom, margin-left, margin-right.

Points to note when using margin:

　1. Collapse: margin collapse exists between block-level elements. If the element becomes an inline element or an inline block element, it will not collapse. Elements will not collapse if they break out of the standard document flow.

2. Use margin to center the box: margin:0 auto;

When using margin:0 auto to center the box, please note: the box must have a clear width. The box must be in the standard document flow. margin:0 auto centers the box, not the content inside the box.

To center the text in the box, you can use: text-align:center; (left to right: text-align:left/right;)

Tips: If you want to move the child elements position, it is recommended to use the padding of the parent element instead of the margin of the child element unless necessary. If margin must be used, the parent element must have a border

Usage guidelines: When using CSS, try as much as possible abbreviation.

padding:10px 20px; means the top and bottom padding is 10px, and the left and right padding is 20px.

padding:10px 20px 30px; means the top padding is 10, the bottom padding is 30px, and the left and right padding is 20px.

padding: 10px 20px 30px 40px; means top, right, and left respectively. Bottom, left padding.

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