Talk about the 8 properties of background in CSS

Like I mentioned before, each element in the document tree is just a rectangular box. These boxes have a background layer, which can be completely transparent or another color, or it can be a picture. This background layer is controlled by 8 CSS properties (plus 1 abbreviated property).

background-color

The background-color property sets the background color of the element. Its value can be any legal color value or the transparent keyword.

.left { background-color: #ffdb3a; }.middle { background-color: #67b3dd; }.right { background-color: transparent; }

The background color is drawn within the area of ​​the box model specified by the [background-clip] (#backgroundclip) attribute. If any background images are also set, the color layer is drawn behind them. Unlike image layers, which can have multiple, we can only have one color layer for an element.

background-image

The background-image attribute defines one or more background images for the element. Its value is usually the url of the image defined with url() notation. You can also use none as its value, but this will generate an empty background layer

.left { background-image: url('ire.png'); }.right { background-image: none; }

We can also specify multiple background images separated by commas. Subsequent pictures will be drawn behind the previous picture in the Z-axis direction.

.middle { 
  background-image: url('khaled.png'), url('ire.png');

  /* Other styles */
  background-repeat: no-repeat; 
  background-size: 100px;}

background-repeat

The background-repeat attribute controls the size of the background image when it is changed by the [background-size] (#backgroundsize) attribute and [ background-position] (#backgroundposition) property how to tile after positioning.

The value of this attribute can be repeat-x, repeat-y, repeat, space, round, no-repeat keywords. In addition to repeat-x and repeat-y, other values ​​can be x-axis and y-axis. Define it once, or you can define each dimension individually.

.top-outer-left { background-repeat: repeat-x; }.top-inner-left { background-repeat: repeat-y; }.top-inner-right { background-repeat: repeat; }.top-outer-right { background-repeat: space; }.bottom-outer-left { background-repeat: round; }.bottom-inner-left { background-repeat: no-repeat; }.bottom-inner-right { background-repeat: space repeat; }.bottom-outer-right { background-repeat: round space; }

background-size

The background-size attribute defines the size of the background image. Its value can be a keyword, length or percentage.

The keywords available for this attribute are "contains" and "cover". contain will scale the image proportionally to its maximum size. Cover, on the other hand, will scale the image to the smallest possible size, where the entire background area is still covered.

.left { 
  background-size: contain;
  background-image: url('ire.png'); 
  background-repeat: no-repeat;}.right { background-size: cover; /* Other styles same as .left */ }

For length and percentage, we can specify the width and height of the background image at the same time, and the percentage value is calculated based on the size of the element.

.left { background-size: 50px; /* Other styles same as .left */ }.right { background-size: 50% 80%; /* Other styles same as .left */ }

background-attachment

background-attachment属性控制控制背景图像相对于视口和元素的滚动方式 。它有三个潜在的值。

fixed意味着背景图片固定在视口并且不会移动，即使用户正沿着视口滚动。local意味着背景图片固定在它在元素中的位置。如果这个元素可以滚动并且背景图片定位在顶部，那么当用户向下滚动这个元素，背景图片将会从视图中滚出去。最后scroll意味着背景图片是固定的且不会随着元素内容的滚动而滚动。

.left { 
  background-attachment: fixed;
  background-size: 50%;
  background-image: url('ire.png'); 
  background-repeat: no-repeat;
  overflow: scroll;}.middle { background-attachment: local; /* Other styles same as .left */ }.right { background-attachment: scroll; /* Other styles same as .left */ }

background-position

这个属性结合background-origin属性定义背景图片的起始位置应在何处。它的值可以是关键字，长度或者百分比，我们可以指定沿x轴和y轴的位置。

可用于此属性的关键字为top, right, bottom, left, 和center，我们可以任意组合这些关键字，如果只明确指定了一个关键字，那么另外一个默认就是center。

.top-left { 
  background-position: top;
  background-size: 50%;
  background-image: url('ire.png'); 
  background-repeat: no-repeat;}.top-middle { background-position: right;  /* Other styles same as .top-left */ }.top-right { background-position: bottom;  /* Other styles same as .top-left */ }.bottom-left { background-position: left;  /* Other styles same as .top-left */ }.bottom-right { background-position: center;  /* Other styles same as .top-left */ }

对于长度和百分比，我们也可以指定沿x轴和y轴的位置。百分比值是按元素的大小计算的。

.left { background-position: 20px 70px; /* Others same as .top-left */ }.right { background-position: 50%; /* Others same as .top-left */ }

background-origin

background-origin属性指定背景图片应根据盒模型的哪个区域进行定位。

当值为border-box时，背景图片的位置根据边框区域定位，为padding-box时其位置根据边距区域定位，为content-box时其位置根据内容区域定位。

.left { 
  background-origin: border-box;
  background-size: 50%;
  background-image: url('ire.png'); 
  background-repeat: no-repeat;
  background-position: top left; 
  border: 10px dotted black; 
  padding: 20px;}.middle { background-origin: padding-box;  /* Other styles same as .left*/ }.right { background-origin: content-box;  /* Other styles same as .left*/ }

background-clip

background-clip属性确定背景绘制区域，这是背景可以被绘制的区域。和background-origin属性一样，它也 基于盒子模型的区域。

.left{ 
  background-clip: border-box;
  background-size: 50%;
  background-color: #ffdb3a; 
  background-repeat: no-repeat;
  background-position: top left; 
  border: 10px dotted black; 
  padding: 20px;}.middle { background-clip: padding-box;  /* Other styles same as .left*/ }.right { background-clip: content-box;  /* Other styles same as .left*/ }

background

Finally, the background attribute is shorthand for other background-related attributes. The order of the subproperties does not matter because the data type of each property is different. However, for background-origin and background-clip, if only one box model area is specified, this value will be applied to both properties. If two are specified, the first value will be used for the background-origin attribute.

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