CSS3 box size

CSS3 box size

CSS3 box-sizing property can set the width and height properties, which include padding (inner margin) and border (border).

Do not use CSS3 box-sizing property

By default, the width and top end of an element are calculated as follows:

width (width) + padding (padding) + border (border) = the actual width of the element

height (height) + padding (padding) + border (border) = the actual height of the element

This means When we set the width/height of an element, the actual displayed height and width of the element will be larger (because the element's border and padding are also calculated in width/height).

     
  
这个是个较小的框 (width 为 300px ，height 为 100px)。
 
 
这个是个较大的框 (width 为 300px ，height 为 100px)。
  

Using this method, if you want to get a smaller box and include padding, you have to consider the width of the border and padding.

The box-sizing property of CSS3 solves this problem very well.

Use the CSS3 box-sizing property

The CSS3 box-sizing property includes padding (inside) in the width and height of an element margin) and border (border).

If box-sizing: border-box; is set on the element, padding (inner margin) and border (border) are also included in width and height:

     
  
两个 div 现在是一样大小的!
 
 
php中文网!
  

From the results See box-sizing: border-box; for better results, which is exactly what many developers need.

The following code can display the size of all elements in a more intuitive way. Many browsers already support box-sizing: border-box; (but not all - that's why input and text elements with width: 100%; have different widths).

     
  
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提示： 可以尝试移除样式中的 box-sizing 属性，看看会发生什么。注意移除后部分浏览器 input, textarea, 和 submit 按钮的宽度不一致。